Aqueous lithium air batteries

ABSTRACT

Aqueous Li/Air secondary battery cells are configurable to achieve high energy density and prolonged cycle life. The cells include a protected a lithium metal or alloy anode and an aqueous catholyte in a cathode compartment. The aqueous catholyte comprises an evaporative-loss resistant and/or polyprotic active compound or active agent that partakes in the discharge reaction and effectuates cathode capacity for discharge in the acidic region. This leads to improved performance including one or more of increased specific energy, improved stability on open circuit, and prolonged cycle life, as well as various methods, including a method of operating an aqueous Li/Air cell to simultaneously achieve improved energy density and prolonged cycle life.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/588,911, filed Aug. 17, 2012, titled AQUEOUS LITHIUM AIR BATTERIES,(now allowed), which claims priority to U.S. Provisional PatentApplication No. 61/525,634 filed Aug. 19, 2011, titled AQUEOUS LITHIUMAIR BATTERIES; which are incorporated herein by reference in theirentireties and for all purposes.

STATEMENT OF GOVERNMENT SUPPORT

This invention was made with Government support under Award No.:DE-AR0000061 awarded by the Advanced Research Projects Agency—Energy(ARPA-E), U.S. Department of Energy. The Government has certain rightsin this invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates generally to alkali metal/oxygenelectrochemical energy storage cells and in particular embodiments tosecondary Li/Air battery cells and aqueous catholytes for use therein aswell as to methods of operating said cells.

2. Related Art

The large free energy of the reaction between lithium and oxygen hasattracted the interest of battery researchers for decades. At a nominalpotential of about 3 volts, the theoretical specific energy for a Li/Airbattery in a non-aqueous electrolyte is over 11,000 Wh/kg for thereaction forming Li₂O₂ (2Li+O₂=Li₂O₂), and in aqueous electrolytes 5,000Wh/kg for the reaction forming LiOH (Li+¼ O₂+½ H₂O=LiOH), both systemsrivaling the energy density for hydrocarbon fuel cells and far exceedinglithium ion battery chemistry. Indeed, as evidenced by the developmentand commercial success of the Zn/Air battery, the high specific energyfor metal/air chemistries has been long recognized. Li/Air chemistry,however, introduces additional challenges.

Today it is generally recognized that there are two basic approaches toLi/Air battery development depending on whether the electrolyte incontact with the cathode is aqueous or non-aqueous (i.e., aqueous Li/Airor non-aqueous Li/Air).

Abraham et al. were the first to describe a non-aqueous Li/Air batteryusing organic carbonate electrolytes commonly employed for lithiumbatteries. Thereafter, in U.S. Pat. Nos. 7,282,295 and 7,645,543 toVisco et al., for example, improved performance is described based onelectrolyte formulations other than carbonates, and more generallyelectrolytes that, albeit unstable in contact with lithium, were enabledfor use in a Li/Air cell because the lithium anode was isolated fromcontact with the electrolyte by a protective membrane architecture.Notwithstanding those improvements, non-aqueous Li/Air cells can beplagued by the formation of a copious amount of insoluble dischargeproduct that can clog cathode pores, severely limiting both dischargecapacity and cycling stability.

Relative to its non-aqueous counterpart, aqueous Li/Air has its own setof unique challenges. Most prominent of these is the reactivity of barelithium metal in contact with water. As described in U.S. Pat. No.7,645,543 and U.S. Pat. No. 7,282,295, for example, practical aqueousLi/Air batteries depend upon stabilizing the lithium anode (e.g.,lithium metal) in the presence of water and oxygen. Protected lithiumelectrodes suitable for use in aqueous Li/Air batteries are described inU.S. Pat. No. 7,282,295 and U.S. Pat. No. 7,645,543, for example. Theprotected lithium electrodes have protective membranes and protectivemembrane architectures that are stable in water environments and arecapable of discharging into aqueous catholytes. For cells employing aprotected lithium electrode, the aqueous electrolyte in contact with thecathode does not contact the lithium anode, and for this reason isgenerally referred to herein and elsewhere as catholyte, and when thecatholyte solvent system is primarily composed of water it is generallyreferred to as an aqueous catholyte.

Today it is generally accepted that in practice, at least for mostapplications, the lithium anode in an aqueous Li/Air battery cell mustbe protected against direct contact with the aqueous electrolyte.

For Li/Air, the type of catholyte (e.g., aqueous or non-aqueous)employed, and its particular formulation, is determinative of thechemistry taking place at the cathode, and ultimately overall cellperformance. The development and search for improved aqueous catholytesfor Li/Air batteries is not simple, the requirements are several-fold,and the results can often be unpredictable.

SUMMARY OF THE INVENTION

Novel catholyte formulations described herein are suitable for use inaqueous secondary Li (or other alkali metal)/Air battery cells andimprove upon a number of cell performance attributes including cyclelife and specific energy.

Alkali metal/oxygen electrochemical energy storage cells having aqueouscatholytes are described. The instant catholytes comprise water and oneor more evaporative-loss resistant and/or polyprotic active compoundsdissolved in water that partake in the discharge reaction and effectuatecathode capacity for discharge in the acidic region. By use of the termacidic region it is meant that portion (or region) of thedischarge/charge capacity over which the catholyte has a pH less than 7.

In various embodiments the active compound dissolved in the catholyte isan active proton generator that dissociates over the course ofdischarge, thus yielding active protons in the catholyte that partake inthe cell reaction as the discharge proceeds. Typically the active protongenerator is a BrØnsted-Lowry acid. In various embodiments the activeproton generator is an organic acid substantially stable againstevaporative losses, for example having a vapor pressure lower than thatof acetic acid (11.4 mmHg (20° C.)), in particular much lower, such asless than 1 mmHg or less than 10⁻³ mmHg, for example malonic acid(3.2×10⁻⁵ mmHg (25° C.)) or citric Acid (1.66×10⁸ mmHg (25° C.)), andtherefore particularly suitable for use in a Li/Air battery cell inaccordance with the present invention. In some embodiments the activeproton generator is a polyprotic organic acid, having two or more (e.g.,three) acidic protons, and therefore capable of providing additionalcathode capacity for discharge in the acidic region withoutoverburdening the weight of the cell. In some embodiments the activecompound does not provide an active proton. Instead, the active compoundundergoes alkaline hydrolysis via reaction with the alkali that isgenerated during cell discharge.

In various aspects, the invention provides:

-   -   i) aqueous catholytes for use in alkali metal/oxygen        electrochemical energy storage cells, and in particular aqueous        Li/Air secondary battery cells;    -   ii) alkali metal/oxygen electrochemical energy storage cells        comprising the aforementioned inventive aqueous catholytes, and        in particular Li/Air secondary batteries wherein the aqueous        catholyte is resistant to evaporative losses; and    -   iii) methods, such as:        -   a. methods of making the inventive aqueous catholytes and            the instant energy storage cells;        -   b. methods of tuning the pH of the catholyte to improve,            among other parameters, stability of the ion membrane in            contact with the catholyte;        -   c. a method of operating a secondary Li/O₂ battery cell over            a broad range of catholyte pH that includes actively            operating the cell (e.g., discharging and charging the cell)            in both the acidic and basic regions; and        -   d. a method for regenerating the catholyte to promote            reversibility and high capacity cycling stability, the            method involving charging the cell to an acidic state of            sufficient acid strength to dissolve and preferably            decompose lithium carbonate solid products that may have            formed in the basic region, and thus, by this expedient,            recover inactivated lithium trapped there within (or as a            component of) the carbonate salts.

In accordance with the instant invention, a battery cell structureincludes: i) a cathode for electro-reducing/electro-oxidizing molecularoxygen during discharging/charging of the cell; ii) an aqueous catholytehaving completely or partially dissolved therein one or moreevaporative-loss resistant and/or polyprotic chemically active speciesor compounds that partake in the discharge/charge reaction; and iii) aprotected lithium electrode composed of an electro-active lithiummaterial shielded from contact with the aqueous catholyte by a liquidimpervious lithium ion conducting membrane.

The chemically active species may be added to the catholyte to enhanceor improve any number of cell characteristics including cathodecapacity, reversibility, discharge/charge cycling stability, stabilityof the solid electrolyte membrane in contact with the catholyte, watermanagement (especially to prevent catholyte dry out in an open to aircell) and/or to generally improve overall cell performance or improve aparticular performance parameter during active operation (i.e., duringactual discharge and charge) and/or at open circuit during storage priorto initial discharge or at intermittent rest periods over the course ofoperation. By use of the term “prior to initial discharge” it is meantprior to actively operating the cell, which means prior to the initialpassing of electrical current through the cell. For various embodimentswhen describing the catholyte composition it is important to distinguishbetween the composition prior to initial discharge and thereafter, sincethe catholyte composition, including its pH, changes as the dischargeand charge proceed.

Briefly, specific functional advantages provided by the chemicallyactive species (or active compound) in the catholyte include one or moreof the following, each of which is more fully described throughout thespecification:

-   -   i) furnishing active protons into the catholyte via dissolution        of an active compound that, when dissolved or otherwise, is        resistant to evaporative losses and stable in contact with the        ion conductive membrane;    -   ii) simultaneously tuning the pH of the catholyte to enhance        stability with the ion conductive membrane while providing        active protons for discharge in the acidic regime;    -   iii) buffering the catholyte pH over a predetermined discharge        capacity as a mechanism to defer or lessen cell operation in the        basic regime, extend cell capacity derived from the acidic        regime;    -   iv) enabling regeneration of inactivated lithium trapped as an        element in a solid phase alkaline discharge products, such as        carbonate discharge products, and thus improving reversibility        of high capacity Li/Air secondary cells that are operated in        both the acidic and basic regimes;    -   v) simultaneously enhancing chemical stability of the membrane        and water management of cells which are operated open to air        (e.g., for various embodiments of the instant Li/Air cell).

In various embodiments, aqueous catholytes of the present inventioncomprise one or more completely or partially dissolved chemical speciesor compounds that serve to improve one or more Li/Air battery cellperformance characteristics or otherwise improve cell operation and/ormaintenance. These chemical species include the following classes:

-   -   i) mono- and polyprotic organic acids and their acid salts, such        as carboxylic acids represented by the general formula:

-   -   wherein R¹ represents an organic radical, R² represents H or an        organic radical; and R³ represents H or an organic radical. The        organic radical may contain other carboxylic groups; then, the        acid is polyprotic. Examples include malonic acid, glutaric acid        and methylsuccinic acid.    -   ii) functionally substituted carboxylic acids, such as amino        acids and hydroxy acids.    -   iii) carboxylic acid derivatives including acyl halides,        anhydrides, esters, amides, nitriles.    -   iv) lactones;    -   v) esters of inorganic acids;    -   vi) sulfur containing organic acids such as sulfonic acids or        their derivatives such as sulfonamides;    -   vii) phenols (optionally substituted and functionalized);    -   viii) inorganic neutral and acid salts, including mixtures of        said salts;        -   viii-a) inorganic neutral salts derived from a strong acid            and a weak base, e.g. zinc nitrate or magnesium nitrate;        -   viii-b) inorganic acid salts, e.g. lithium dihydrogen            phosphate and lithium hydrogen selenate;    -   ix) amphoteric hydroxides;    -   x) onium salts formed with organic acids    -   xi) onium salts formed with inorganic acids;    -   Onium salts are of the general formula: (R_(n)MH)⁺X⁺ wherein R        may represent hydrogen, and at least one of the R represents an        aliphatic or aromatic optionally substituted organic radical; M        represents elements of the nitrogen group, or chalcogen, or        halogen; X⁻ is organic or inorganic acid residue. When M is        nitrogen, an onium salt is an aminium salt. An aminium salt        where the aminium cation is a primary, secondary, or tertiary        ammonium cation is of the general formula (NHR¹R²R³)⁺ wherein        R¹, R², R³ may represent hydrogen, and at least one of them        represents an aliphatic or aromatic optionally substituted        organic radical.    -   xii) supporting salts of the alkali metal (e.g., supporting        lithium salts).

In various embodiments the aqueous acidic catholyte of the instantinvention comprises water and, dissolved therein, a polyprotic organicacid exemplified by polycarboxylic acid (e.g., diprotic malonic acid andtriprotic citric acid). The carboxylic acid may be functionalized orsubstituted to enhance one or more of the following characteristics:stability to oxidation, acid strength, hygroscopicity of the dissolvedacid and/or that of an acid salt that forms as a result of celldischarge or may be loaded in the catholyte as a partially neutralizedpolyprotic acid and exists in the catholyte as an acid salt or may beloaded in the catholyte as an onium acid or a neutral salt prior toactively operating the cell (i.e., prior to initial discharge).

In various embodiments the aqueous acidic catholyte of the instantinvention comprises water and, dissolved therein, a carboxylic acidrepresented by the general formula

wherein R¹ represents an organic radical, R² represents H or an organicradical; and R³ represents H or an organic radical.

The carboxylic acid represented by formula (1) may be aliphatic oraromatic, monocarboxylic or polycarboxylic. A single composition of acidmay be dissolved in the catholyte; however, combinations of differentcarboxylic acid compositions are contemplated as well.

With continued reference to formula (1), in various embodiments at leastone of R¹, R², and R³ represents an organic radical, and in certainembodiments thereof each of R¹, R², and R³ represents an organicradical. In various preferred embodiments at least one of R¹, R² or R³contains a carboxyl group.

For instance, in some embodiments, at least one of R¹, R² and R³represent an organic radical selected from the group consisting of anoptionally substituted C₁-C₁₀ alkyl group, optionally substituted C₂-C₁₀alkenyl group, optionally substituted C₂-C₁₀ alkynyl group. As usedherein a “substituted group” is derived from the unsubstituted parentstructure in which there has been an exchange of one or more hydrogenatoms for another atom or group. In other embodiments, at least one ofR¹, R² and R³ represents an organic radical selected from the groupconsisting of an optionally substituted C₄-C₁₀ cycloalkyl, optionallysubstituted C₄-C₁₀ cycloalkenyl, and optionally substituted 3-10membered heterocyclyl. In yet other embodiments at least one of R¹, R²and R³ represent an organic radical selected from the group consistingof an optionally substituted carbo- and heterocyclic 5-10 membered aryl.

In various embodiments the carboxylic acid is malonic acid, glutaricacid, methylsuccinic acid, or some combination thereof (e.g., malonicacid wherein, with reference to formula (1), R² and R³ represent H andR¹ represents carboxyl group).

In various embodiments the aqueous acidic catholyte of the instantinvention comprises water and, dissolved therein, a “functionallysubstituted” carboxylic acid for instance an amino acid or hydroxy acid.

In various embodiments a weak Lewis base having an atom with a loneelectron pair reacts with an organic or inorganic mono- or polyproticacid to form an onium salt, and more particularly an aminium salt,wherein one or more of the acidic protons originally attached to theacid are transferred to one or more weak Lewis base molecules.

In various embodiments the functionally substituted carboxylic acid isan amino acid, such as that containing an amine group, a carboxylicgroup, and an organic radical. In embodiments the amino acid has thefollowing general formula

wherein R represents an aliphatic or aromatic optionally substitutedorganic divalent radical.

Amino acids and the like are advantageous because they may be used inthe form of aminium salt where besides the protonated amino group orgroups, it also has the acidic proton on the carboxylic group. In thecase of such aminium salt, the molecular mass/active proton ratio canincrease. For instance, as illustrated below, an amino acid aminium saltconsumes two moles of alkali per one mole of amino acid aminium salt,

wherein X may be NO₃ ⁺, SO₄ ²⁻, ClO₄ ⁻.

Suitable amino acids include glycine, alanine, valine, proline,hydroxyproline, histidine, cysteine, serine, glutamine, lysine,hydroxylysine, arginine, methionine, asparagine, phenylalanine, andaminomalonic acid. For example glycine, alanine, and proline.

In various embodiments the functionally substituted carboxylic acid is ahydroxy acid such as that containing a hydroxy group, a carboxylic groupand an organic radical.

In embodiments, the hydroxy acid has the following general formula

wherein R represents an aliphatic or aromatic organic divalent radical.

Suitable hydroxy carboxylic acids include citric acid, glycolic acid,lactic acid, 2-hydroxypropionic acid, 3-hydroxypropionic acid,2-hydroxybutyric acid, 3-hydroxybutyric acid, and the like (e.g., citricacid).

In various embodiments the aqueous catholyte of the instant inventioncomprises water and, dissolved therein, a “carboxylic acid derivative”such as that represented by the general formula

-   -   wherein R represents an organic aliphatic or aromatic group that        may contain other COX groups if a compound is, for example, a        polycarboxylic acid derivative, and X may be, but is not limited        to, one of the following    -   X=Halogen (F, Cl, Br, I)—acyl halides;    -   X═OC(R¹)═O—anhydrides where R¹=an organic aliphatic or aromatic        group;    -   X═OR²—esters where R²=an organic aliphatic or aromatic group;    -   X=N(R³R⁴)—amides where R³, R⁴=H, an organic aliphatic or        aromatic groups.    -   Or nitrile represented by the general formula

R—CN,

-   -   where R is an organic aliphatic or aromatic radical.

Accordingly, in various embodiments the carboxylic acid derivative maybe an acyl halide, an anhydride, an ester, an amide, or a nitrile (e.g.,an ester of carboxylic acid).

Suitable organic esters include those having represented by thefollowing general formula

wherein

-   -   R¹=benzyl, phenyl, —COOR, —CH₂COOR, —CH₂CH₂COOR, —CH₂CH₂CH₂COOR,        —CH₂CN, —CH₂CF₃, CCl₂, C₅H₁₁, C₆H₁₃, etc.;    -   R²=—CH₂—CH₂OH, —CH₂—CH₂OR, —CH₂—CH(OH)—CH₂OH, —CH₂—CH(OR)—CH₂OH,        —CH₂—CH(OH)—CH₂OR, —CH₂—CH(OR)—CH₂OR, —(CH₂)₂—O—(CH₂)₂OR;    -   R=organic aliphatic or aromatic group.

Some of the more preferred esters are diethylene glycol dibenzoate,2-methoxyethyl cyanoacetate, ethylene glycol monosalicylate, andethylene brassylate.

When added to the catholyte, esters undergo alkaline hydrolysis(sometimes referred to as saponification) via reaction with the celldischarge product (LiOH), as illustrated below

The rate of alkaline hydrolysis relative to that of neutral and acidichydrolysis that may take place prior to cell discharge depends onsubstituents R₁ and R₂. The more electron withdrawing inductive effectof the substituent, the higher the hydrolysis rate becomes. Substituentsare generally chosen to decrease (e.g., minimize) the rate of neutraland acidic hydrolysis and increase (e.g., maximize) the rate of alkalinehydrolysis.

In various embodiments the carboxylic acid derivative is a lactone, suchas those represented by the general formula

wherein n may be 2 or 4.

wherein R¹ represents an aliphatic or aromatic optionally substitutedorganic radical; and

wherein R² represents an aliphatic or aromatic optionally substitutedorganic radical.

Lactones dissolved in water may be in equilibrium with the correspondinghydroxy acid as illustrated below. Equilibrium depends on pH and thesubstituent groups R₁, R₂. At high pH values equilibrium may bedramatically shifted toward lactone cycle opening.

Suitable lactones include γ-butyrolactone, δ-gluconolactone, andglutaric anhydride.

In various embodiments the aqueous catholyte of the instant inventioncomprises water and, completely or partially dissolved therein, aphosphate ester, such as those represented by the general formula

wherein: R¹=aliphatic or aromatic group; R², R³ is an aliphatic oraromatic optionally substituted organic radical, or hydrogen atom.

Phosphate triesters (R², R³ is an aliphatic or aromatic optionallysubstituted organic radical) and diesters (one of the R², R³ is hydrogenatom and the other one is an aliphatic or aromatic optionallysubstituted organic radical) are particularly suitable in someembodiments.

Particularly suitable phosphate triesters include trimethyl phosphate,triethyl phosphate, tripropyl phosphate, tributyl phosphate, andtris(2-butoxyethyl) phosphate.

In various embodiments the aqueous catholyte of the instant inventioncomprises water and, completely or partially dissolved therein, an esterof inorganic acid represented by the general formula X(OR)_(n)

wherein R is an aliphatic or aromatic optionally substituted organicradical; and

X=N(═O)₂, S(═O)₂, P═O

n is basicity of an acid from which the ester was derived

In various embodiments the aqueous catholyte of the instant inventioncomprises water and, completely or partially dissolved therein, an esterof sulfuric acid that is represented by the general formula:

wherein R¹ is an aliphatic or aromatic optionally substituted organicradical; and

wherein R² is an aliphatic or aromatic optionally substituted organicradical.

In various embodiments the aqueous catholyte of the instant inventioncomprises water and, completely or partially dissolved therein, an esterof nitric acid that is represented by the general formula:

wherein R is an aliphatic or aromatic optionally substituted organicradical.

In various embodiments the aqueous catholyte of the instant inventioncomprises water and, dissolved therein, a sulfur-containing organiccompound such as sulfonic acid or an amide of sulfonic acid (i.e., asulfonamide). For instance, a sulfonic acid represented by the generalformula

wherein R represents an organic aliphatic or aromatic group.Or sulfonamides represented by the general formula

wherein R¹, R²=an organic aliphatic or aromatic group.

Suitable sulfonic acids include MES (2-(N-Morpholino)ethanesulfonicacid), MOPS (3-(N-Morpholino)propanesulfonic acid), BES(N,N-Bis(2-hydroxyethyl)-2-aminoethanesulfonic acid), TES(2-[(2-Hydroxy-1,1-bis(hydroxymethyl) ethyl)amino]ethanesulfonic acid),TAPSO (2-Hydroxy-3-[tris(hydroxymethyl)methylamino]-1-propanesulfonicacid), N-[Tris(hydroxymethyl) methyl]-3-amino-2-hydroxypropanesulfonicacid), HEPPS (4-(2-Hydroxyethyl)-1-piperazinepropanesulfonic acid), CHES(2-(Cyclohexylamino) ethanesulfonic acid), 3-Aminobenzenesulfonic acid;for example MES, MOPS, and HEPPS.

Suitable sulfonamides include o-, m-, p-aminobenzenesulfonamides, o-,m-, p-methylbenzenesulfonamides, o-, m-, p-cyanobenzenesulfonamides,4,4′-diaminobenzenesulphanilide.

In various embodiments the aqueous catholyte of the instant inventioncomprises water and, dissolved therein, a phenol. Phenols are organiccompounds containing an hydroxyl group directly attached to an aromaticcarbon atom, and may be represented by the general formula

Wherein R¹, R², R³, R⁴, R⁵=H, OH, CH₃, C₂H₅, C₃H₇, NH₂, NO₂, CN, COOH,SO₃H, C(R)═O, F, Cl, Br, I, CF₃, NR₃ ⁺, COOR, CONH₂, CCl₃, OR, NR₂; andR represents H, or an aliphatic or aromatic organic radical.

Phenol acidity and electrooxidation potential both depend on itssubstituents. The oxidation potential of substituted phenols becomesmore positive, and pK_(a) values become more negative with an increaseof Hammett's constant value of the corresponding substituent. In otherwords, the direct electrochemical oxidation of substituted phenol withan electron-withdrawing group is more difficult, and acidity is higherthan that of substituted phenol with an electron-donating group.

Particularly suitable phenols include resorcinol, 2-methylresorcinol,gallic acid, 4-nitrocathecol, 4-hydroxybenzoic acid, 2-nitroresorcinol;for example, α-resorcylic acid, α-resorcylonitrile.

In various embodiments the aqueous catholyte of the instant inventioncomprises water and, dissolved therein, an aminium salt formed withinorganic acid. For instance, a salt represented by the followinggeneral formula (HNR¹R²R³)⁺X⁻, wherein X⁻ represents an inorganic acidresidue and R¹, R², R³ may represent hydrogen atom, and at least one ofthem represents an aliphatic or aromatic optionally substituted organicradical. The aminium salt is preferably selected from chloride, sulfate,perchlorate salts, and even more preferably is a nitrate.

Particularly suitable such salts include aniline nitrate,diethylenetriamine nitrate, ethanolamine nitrate, 2-methyl-1-pyrrolinenitrate, methoxyamine nitrate, N-methoxymethylamine nitrate,1-benzoylpiperazine nitrate, N-methylhydroxylamine nitrate,2-aminocyanopropane nitrate, N,N-diethylcyanoacetamide nitrate,dimethylaminoacetonitrile nitrate, 2,2-diethylaminopropionitrilenitrate, 2-amino-2-cyanoproapne, piperazine dinitrate,N,N-dimethylethylenediamine dinitrate, N-ethylmorpholine nitrate, andtriethanolamine nitrate.

Alternatively, the aminium salt may be based on a N-heterocyclicaromatic compound such as imidazole. Particularly suitable such saltsinclude imidazolium nitrate, 2-methylimidazolium nitrate,4-hydroxymethyl imidazolium nitrate, 4-hydroxybenzimidazolium nitrate,4-methoxybenzimidazolium nitrate, 4-(N-methylacetamido)pyridiniumnitrate, o-, m-, p-methylpyridinium nitrate, o-, m-, p-ethylpyridiniumnitrate, 2-methoxypyridinium nitrate, 3-methoxypyridinium nitrate,3-hydroxypyridinium nitrate, 4-hydroxypyridinium nitrate,3-fluoropyridinium nitrate, 3-bromopyridinium nitrate,3-sulfoxypyridinium nitrate, 3-aminopyridazinium nitrate,3-carboxypyridinium nitrate, 4-methoxypyridazinium nitrate, and2-amino-4,6-dimethyl pyrazinium nitrate; for example, imidazoliumnitrate.

In yet other alternative embodiments the aminium salt may be an ammoniumsalt. For instance, that which is represented by the general formula(NH₄ ⁺)X⁻, wherein X⁻ is an acid residue.

In various embodiments the aqueous catholyte of the instant inventioncomprises water and, dissolved therein, one or more inorganic neutral oracid salts.

Particularly suitable neutral salts include nitrate salts derived from astrong acid and a weak base, e.g., zinc nitrate or magnesium nitrate.

In various embodiments the catholyte contains, dissolved therein, two ormore of such salts of different composition. For instance a first saltof magnesium nitrate and a second salt of zinc nitrate. Dissolved in thecatholyte, the concentration of the respective salts may be adjusted totune the pH of the catholyte to pH values suitable to decompose lithiumcarbonate solid product precipitates that may form in alkalinecatholytes during exposure to ambient air whence the cell deeplydischarged into the basic region. For instance, the inventors havediscovered that concentrations greater than or equal to 2 molar (e.g.,between 2-3 molar) of a first such said salt (e.g., magnesium nitrate)and 0.1 to 1 molar of a second such said salt of different composition(e.g., zinc nitrate) yields a catholyte formulation capable of providingsuch benefit. Typically, the magnesium salt (i.e., first salt) ispresent in concentration to about five times the value of the zinc salt(i.e., second salt). Accordingly, in various embodiments, to enabledecomposition of carbonate discharge products on charge, said nitratesalts are dissolved in appropriate proportions to render the startingcatholyte pH between 3 and 4, and preferably between 3.1 and 3.8, e.g.,about 3.5).

Particularly suitable inorganic acid salts include salts such as lithiumdihydrogen phosphate or lithium hydrogen selenate.

In yet other embodiments, the catholyte comprises an amphoterichydroxide, or combination of two or more different hydroxides, such aszinc hydroxide and aluminum hydroxide sols that provide similar benefit,as described above, or other benefit to the cell chemistry. Forinstance, from about 0.5 M to 4.0 M to of zinc hydroxide and aluminumhydroxide).

Furthermore, zinc nitrate mentioned above may be used as a precursor ofzinc hydroxide. As a result of reaction with the cell discharge product(lithium hydroxide), zinc nitrate converts into zinc hydroxide, whichthen reacts with lithium hydroxide forming a well soluble product in theform of dilithium tetrahydroxyzincate. Thus, four moles of alkali areconsumed per one mole of zinc nitrate in acidic and basic regimes ofcell discharge as described below:

2Li⁺+Zn(NO₃)₂+½O₂+H₂O+2e→Zn(OH)₂+2LiNO₃

2Li⁺+Zn(OH)₂+½O₂+H₂O+2e→Li₂[Zn(OH)₄]

In various embodiments the catholyte comprises a supporting Li salt tomaintain conductivity of catholyte at different stages of discharge. Ithas also been found that introduction of certain concentrations of Lisupporting salts, can prevent resistance rise during storage under opencircuit conditions. For this purpose, initial (prior to initialdischarge) Li cation concentrations of at least 1M, for example 1M andup to 4M, can be effectively used. While the invention is not limited byany particular theory of operation, this effect is attributed to thesuppression of ion exchange at the interface between protective membraneand liquid catholyte. Hygroscopic supporting Li salts can be used inorder to maintain moisture balance in the cell before the start ofdischarge. This is one more function of supporting Li salts.Particularly preferred supporting salts include lithium nitrate, e.g.,LiNO₃. The supporting salts are typically included in the catholyte inaddition to any other chemical species or compound, such as, but notlimited to, polyprotic organic acids and carboxylic acid derivatives andphosphate esters.

In other aspects, methods are provided. In particular, these includemethods of making the aforementioned catholytes and battery cells and anovel method of operating a Li/Air secondary battery cell that enhanceselectrochemical reversibility when the cell is discharged over both theacidic and basic regimes for added cathode capacity. The methodgenerally includes the steps of:

-   -   i) providing an aqueous catholyte having a sufficient acid        strength to cause decomposition of lithium carbonate;    -   ii) discharging the cell from the acidic regime into the basic        regime, and optionally to full or nearly full discharge        capacity;    -   iii) subsequently charging the cell into the acidic regime to a        capacity that renders the pH of the catholyte sufficient to        dissolve and decompose lithium carbonates formed in the cathode        compartment; and    -   iv) optionally whence the catholyte has reached or is estimated        to have reached the prescribed necessary acidity to decompose        carbonate, maintaining the cell at a given voltage or current        over a time period sufficient to recover most or all of the        initial cell capacity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic illustration of a Li/air battery cell inaccordance with the present invention.

FIG. 1B shows a Li/air battery cell in accordance with the presentinvention enclosed in a cell case in cross sectional and perspectivedepictions.

FIGS. 2A-D illustrate various alternative configurations of a protectivemembrane architecture in accordance with the present invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS Introduction

Alkali metal/oxygen electrochemical energy storage cells having aqueouscatholytes are described. The instant catholytes comprise water and oneor more evaporative-loss resistant and/or polyprotic active compoundscompletely or partially dissolved in water that partake in the dischargereaction and effectuate cathode capacity in the acidic regime. Invarious embodiments the active compound is an active proton generatorthat whence dissolved in water dissociates over the course of celldischarge to yield active protons in the catholyte that partake in thedischarge reaction. Typically the active proton generator is aBrønsted-Lowry acid. In various embodiments the active proton generatoris an organic acid stable against evaporative losses and thereforeparticularly suitable for use in a Li/Air battery cell of the instantinvention. In various embodiments the active proton generator is apolyprotic organic acid, having two or more (e.g., three) acidicprotons, and therefore capable of providing additional cathode capacityin the acidic regime without unduly adding extra weight to the cell. Insome embodiments the active compound does not directly provide an activeproton. Instead, it undergoes alkaline hydrolysis with alkali formedduring cell discharge.

In various aspects the invention provides:

-   -   i) alkali metal/oxygen electrochemical energy storage cells        comprising the aforementioned inventive aqueous catholytes, and        in particular Li/Air secondary batteries wherein the aqueous        catholyte is resistant to evaporative losses;    -   ii) aqueous catholytes for use in alkali metal/oxygen        electrochemical energy storage cells, and in particular aqueous        Li/Air secondary battery cells; and iii) methods, such as:        -   a. methods of making the inventive aqueous catholytes and            the instant energy storage cells;        -   b. methods of tuning the pH of the catholyte to improve,            among other parameters, stability of the ion membrane in            contact with the catholyte.        -   c. a method of operating a secondary Li/O₂ battery cell over            a broad range of catholyte pH that includes discharging and            charging the cell through both the acidic and basic regimes;            and        -   d. a method for regenerating the catholyte to promote            reversibility and high capacity cycling stability, the            method involving charging the cell to an acidic state            sufficient to dissolve and decompose lithium carbonate solid            products, and thus recover inactivated lithium trapped there            within the carbonate salt.

In accordance with the instant invention, the battery cell structureincludes: i) a cathode for electro-reducing of molecular oxygen duringdischarging and electro-oxidizing of water during charging of the cell;ii) an aqueous catholyte having dissolved therein one or moreevaporative-loss resistant and/or polyprotic chemically active speciesor compounds that partake in the discharge/charge reaction; and iii) aprotected lithium electrode composed of an electro-active lithiummaterial shielded from contact with the catholyte by a liquidimpermeable lithium ion conducting membrane.

Because the catholyte is aqueous it is essential to keep it out ofdirect contact with the electroactive lithium. Various schemes may beused to provide such protection. Non-limiting examples of protectionmethods and protected electrode structures that are suitable for useherein and are fully described in U.S. Pat. No. 7,282,296; U.S. Pat. No.7,858,223; U.S. Pat. No. 7,645,543; U.S. Pat. No. 7,390,591; U.S. Pat.No. 7,282,295; and U.S. Pat. No. 7,824,806, and each of these is herebyfully incorporated by reference for all that they describe. Generally,the protected electrode contains a lithium ion conductive liquidimpermeable membrane that is chemically compatible on one side incontact with the catholyte and on the other side in contact with theelectroactive lithium. To protect the edges, rigid or compliant sealsmay be incorporated as are described in U.S. Pat. No. 7,284,806 and U.S.Patent Publication No. 2008/0182157, which are hereby incorporated byreference for all that they describe in this regard.

Two approaches for the development of secondary aqueous lithium airbattery chemistry have been described depending on whether the startingcatholyte is acidic or neutral:

The first approach makes use of what is generally termed a neutralcatholyte solution, typically composed, in its most simplified form, ofa supporting lithium salt dissolved in water; the supporting saltserving to support the ionic current through the catholyte duringpassage of current. The pH of neutral catholyte is about 7, but becomesalkaline almost immediately upon discharge as base (LiOH) is producedaccording to the following reaction:

2Li+½O₂+H₂O

2LiOH

In neutral or alkaline solutions, base formed on discharge causes thecell to immediately enter or remain in the basic regime. Lithiumhydroxide solution is known to react with carbon dioxide from ambientenvironment and form poorly soluble lithium carbonate:

2LiOH+CO₂

Li₂CO₃+H₂O

Since lithium carbonate is highly insoluble in neutral, alkaline, andeven moderately acidic solutions, active lithium ions can become trappedin highly insoluble solid carbonate products that may form during deepdischarge and which may also form during cell resting periods (e.g., atopen circuit) in strongly basic catholyte. In both instances theformation of solid carbonate product can render a portion of the initiallithium capacity inactive, leading to capacity fade which can besignificant even after just a few cycles (e.g., 1-3 cycles).

If oxygen is used from an external source other than the ambientatmosphere, such as a tank of O₂ gas (or air) that is devoid of CO₂,carbonate degradation can be avoided. But for a Li/Air cell, which isopen to ambient air, CO₂ generally enters the catholyte along with theactive O₂. Accordingly, it is contemplated, herein, that the ingress ofCO₂ relative to that for O₂ may be reduced, and preferably entirelyeliminated, by using a highly selective O₂ semi-permeable membranebetween the cathode and the ambient air, even though, at the presenttime, such schemes may be impractical or prohibitively expensive. Thus,the reversibility of Li/Air cells discharged into the basic regime, andespecially if discharged deeply enough to precipitate a copious amountof LiOH, are challenged by the aforementioned carbonate reactionproducts and the concomitant loss of active lithium.

To provide a more reversible Li/Air cell, a second approach may be takenwhich is to use an acidic catholyte and exclusively cycle the cell inthe acidic regime to circumvent base and the generally irreversibleformation of insoluble solid lithium carbonate salts. Li/Air dischargein acidic catholyte is generally understood by the following cellreaction.

2Li+½O₂+2HA

2LiA+H₂O

Maintaining operation in the acidic regime avoids accumulation of LiOHand is generally deemed more desirable than the first approach from theperspective of reversibility, cycle life, and service life. However thesecond approach has a considerably lower theoretical energy densitybecause of the additional weight of the acid. For instance, twice thenumber of moles of acid is required when discharging in the acidicregime relative to the number of moles of water consumed duringdischarge in alkaline. From the singular perspective of energy density(or specific gravity), a strong, relatively lightweight inorganic acidis preferred. However, such acids, precisely because of their acidstrength, can destabilize the ion conductive membrane yielding very lowpH values (e.g., below 3 or 2). Furthermore, low molecular weight acids(strong or otherwise, e.g., weak) though seemingly desirable from theperspective of energy density, are generally volatile and thussusceptible to evaporative losses and therefore may be unsuitable, or atleast less desirable, for use in open to air cells such as Li/Airdeployed in a wide variety of use applications requiring long servicelife or deployed under circumstances that may accelerate evaporation ofthe acid.

Accordingly, the first and second approaches to aqueous Li/Air each havetheir own particular advantages and disadvantages.

In one aspect, the present invention describes a third approach ormethod of operating a Li/Air battery cell. The method includes providinga secondary Li/O₂ battery cell, and in particular a Li/Air cell, thatcan be reversibly cycled over both the acidic and basic regimes, and bythis expedient said cells have increased cathode capacity per unitweight, and improved energy density.

In various other aspects the invention provides:

-   -   i) aqueous catholytes for use in alkali metal/oxygen        electrochemical energy storage cells, and in particular aqueous        Li/Air batteries;    -   ii) alkali metal/oxygen electrochemical energy storage cells        comprising the said aqueous catholytes;    -   iii) methods, such as:        -   a. methods of making said aqueous catholytes and said energy            storage cells.        -   b. methods of tuning the pH of the catholyte to improve            stability of the membrane in contact with the catholyte.        -   c. methods of operating a secondary Li/O2 battery cell over            a broad range of pH regimes, inclusive of both the acidic            and basic regimes, and methods thereof for regenerating the            catholyte to promote reversibility and high capacity cycling            stability.

The active compound may be added to the catholyte to enhance any numberof cell performance parameters, including: cathode capacity,reversibility, discharge/charge cycle stability, ion membrane stability,water management and/or to generally improve overall cell performance ora particular performance parameter, including performance during activeoperation (i.e., during actual discharge and charge) and/or upon opencircuit during storage prior to operation or as a result of intermittentrest periods over the course of operation. In various embodiments theactive compound in the catholyte may serve one or more functions,including:

furnishing active protons into the catholyte via dissolution of anactive compound that, whence dissolved or otherwise, is resistant toevaporative losses and stable in contact with the ion conductivemembrane;

simultaneously tuning the pH of the catholyte to enhance stability withthe ion conductive membrane while providing active protons for dischargein the acidic regime (i.e., that portion of the discharge/chargecapacity over which the catholyte has a pH less than 7);

buffering the catholyte pH over a predetermined discharge capacity as amechanism to defer or lessen cell operation in the basic regime (i.e.,that portion of the discharge/charge capacity over which the catholytehas a pH greater than 7);

enabling regeneration of inactivated lithium ions in a solid phase ofcarbonate discharge product, and thus improving reversibility of highcapacity Li/Air secondary cells that are operated in both the acidic andbasic regimes;

simultaneously enhancing chemical stability of the membrane and watermanagement of cells which are operated open to air (e.g., variousembodiments of the instant Li/Air cell).

Reference will now be made in detail to specific embodiments of theinvention. Examples of the specific embodiments are illustrated in theaccompanying drawings. While the invention will be described inconjunction with these specific embodiments, it will be understood thatit is not intended to limit the invention to such specific embodiments.On the contrary, it is intended to cover alternatives, modifications,and equivalents as may be included within the spirit and scope of theinvention. In the following description, numerous specific details areset forth in order to provide a thorough understanding of the presentinvention. The present invention may be practiced without some or all ofthese specific details. In other instances, well known processoperations have not been described in details so as to not unnecessarilyobscure the present invention.

When used in combination with “comprising: “a method comprising,” “adevice comprising” or similar language in this specification and theappended claims, the singular forms “a,” “an, and “the” include pluralreference unless the context clearly dictates otherwise. Unless definedotherwise, all technical and scientific terms used herein have the samemeaning as commonly understood to one of ordinary skill in the art towhich this invention belongs.

In the figures, like reference numbers indicate identical orfunctionally similar elements.

Cell Structure

A battery cell in accordance with the current invention is schematicallyshown in FIG. 1A. The cell comprises a Li anode 1 protected with aprotective membrane architecture chemically stable to both the anode andthe environment of an adjacent cathode compartment 4. The protectivemembrane architecture typically comprises a solid electrolyte protectivemembrane 2 and an interlayer 3. The protective membrane architecture isin ionic continuity with the Li anode 1 and is configured to selectivelytransport Li ions into and out of the cathode compartment 4 whileproviding a substantially impervious barrier to the environment externalto the anode. The cathode compartment 4 comprises an air cathode 5 (alsosometimes referred to herein as an “oxygen electrode”) and an aqueouscatholyte 6, which is disposed between the cathode 5 and the solidelectrolyte protective membrane 2 and is in direct contact with thecathode 5 for reducing molecular oxygen, and is also typically incontact with a surface of the solid electrolyte membrane 2. The cathodecompartment 4 can further comprise one or more porous solid reservoirstructures 7 disposed between the solid electrolyte protective membrane2 and the air cathode 5. The aqueous catholyte 6 and porous solidreservoir 7 are represented as separate layers in FIG. 1A for ease ofillustration, however they may be and often are co-extensive in manyembodiments of the invention. The aqueous catholyte, in contact with thecathode, does not contact the Li anode.

Aqueous Catholytes

In various embodiments, the aqueous catholyte 6 is an aqueous solutionof water and at least one evaporative-loss resistant and/or polyproticactive compound that, dissolved in water, partakes in the dischargereaction at the cathode in the acidic region.

Typically a lithium salt is also dissolved in the catholyte to supportthe ionic current and in some embodiments may provide the additionalbenefit of water management to prevent dry out of a Li/Air cell. Theactive compound may be one or more of the following compounds:

i) mono- and polyprotic organic acids and their acid salts, such ascarboxylic acids represented by the general formula:

wherein R¹ represents an organic radical, R² represents H or an organicradical; and R³ represents H or an organic radical. The organic radicalmay contain other carboxylic groups; then, the acid is polyprotic.Examples include malonic acid, glutaric acid and methylsuccinic acid.

ii) functionally substituted carboxylic acids, such as amino acids andhydroxy acids. As used herein a “substituted” group is derived from theunsubstituted parent structure in which there has been an exchange ofone or more hydrogen atoms for another atom or group.

iii) carboxylic acid derivatives including acyl halides, anhydrides,esters, amides, nitriles.

iv) lactones;

v) esters of inorganic acids;

vi) sulfur containing organic acids such as sulfonic acids or theirderivatives such as sulfonamides;

vii) phenols (optionally substituted and functionalized);

viii) inorganic neutral and acid salts, including mixtures of saidsalts;

-   -   viii-a) inorganic neutral salts derived from a strong acid and a        weak base, e.g. zinc nitrate or magnesium nitrate;    -   viii-b) inorganic acid salts, e.g. lithium dihydrogen phosphate        and lithium hydrogen selenate;

ix) amphoteric hydroxides;

x) onium salts formed with organic acids

xi) onium salts formed with inorganic acids;

Onium salts are of the general formula: (R_(n)MH)⁺X⁻ wherein R mayrepresent hydrogen, and at least one of the R represents an aliphatic oraromatic optionally substituted organic radical; M represents elementsof the nitrogen group, or chalcogen, or halogen; X⁻ is organic orinorganic acid residue. When M is nitrogen, an onium salt is an aminiumsalt. An aminium salt where the aminium cation is a primary, secondary,or tertiary ammonium cation is of the general formula (NHR¹R²R³)⁺wherein R¹, R², R³ may represent hydrogen, and at least one of themrepresents an aliphatic or aromatic optionally substituted organicradical.

xii) supporting salts of the alkali metal (e.g., supporting lithiumsalts).

In various embodiments, the catholyte includes an active compound thatwhence dissolved in water dissociates over the course of discharge toyield one or more active protons in the catholyte. Typically the activecompound is an organic Brønsted-Lowry acid. When incorporated in an opento air cell the compound should be sufficiently resistant to evaporativelosses, and preferably the relative volatility of the acid in thecatholyte is lower than that of water. That the active compound shouldbe highly resistant to evaporative losses is very important for an opento air cell because while water can ingress into the catholyte from theambient air over the course of cell operation, the same is not true forthe acid or more generally the active compound, regardless of whether it(the active compound) is dissolved in the catholyte or otherwise presentin the cathode compartment in contact with the catholyte (e.g., as asolid phase active compound that is in dynamic equilibrium with itssaturated solution in catholyte). By sufficiently resistant toevaporative losses it is meant that the compound, dissolved in water ofthe catholyte or otherwise, has a sufficiently low vapor pressure thatover the service life of the open to air cell in which it isincorporated the total amount of active compound lost to vaporization isless than 10%, preferably less than 5% and even more preferably lessthan 2%. Various metrics other than vapor pressure may be used to gaugethe relative evaporative resistance of structurally or chemicallysimilar active compounds, these include the compound's boiling pointtemperature and in some instances, where the compounds are structurallysimilar, molecular weight may provide a metric for volatility to someextent.

By use of the term active proton when referring to an active compound itis meant that the compound has at least one acidic proton that partakesin the discharge reaction subsequent to the dissociation of thedissolved active compound. For instance, according to the following cellreaction where n represents the basicity of an acid.

Li⁺+H_(n)A+¼O2+e

H_(n-1)ALi+½H₂O

Li⁺+H_(n-1)ALi+¼O₂ +e

H_(n-2)ALi₂+½H₂O

. . .

Li⁺+HALi_(n-1)+¼O₂ +e

ALi_(n)+½H₂O

Li⁺+¼O₂+½H₂O+e

LiOH

-   -   where H_(n)A is a mono- or polyprotic acid, n=1-5. Preferably,        the formed lithium salt is soluble in water, and even more        preferably the solubility of the salt (ALi_(n) or Li_(n)A) in        water is greater than 1 molar.

In various embodiments an acid residue A may be:

-   -   carboxylic anion RCOO⁻ wherein R represent an aliphatic or        aromatic optionally substituted organic radical;    -   N-containing aliphatic or aromatic compound R¹R²R³N where        nitrogen atom has lone pair of electrons and wherein R¹, R², R³        may represent hydrogen, and at least one of them represent an        aliphatic or aromatic optionally substituted organic radical;    -   arenoxy anion Ar—O⁻;    -   sulfonamide anion;    -   sulfoxide anion

The active compound provides active proton capacity to the cathode viathe catholyte, and full or partial benefit of the inventive catholytemay be derived regardless of whether the cell is a primary or asecondary or exclusively or otherwise operated in the acidic regime,basic regime or both, or some combination thereof. In other words, thereis no limitation regarding the manner in which the battery cell may beoperated in order to derive full or partial benefit from the activecompound.

In various embodiments the active compound is a carboxylic acid havingthe general formula:

wherein R¹ represents an organic radical, R² represents H or an organicradical; and R³ represents H or an organic radical.

The carboxylic acid represented by formula (1) may be aliphatic oraromatic, monocarboxylic or polycarboxylic. A single composition of acidmay be dissolved in the catholyte; however, combinations of differentcarboxylic acid compositions are contemplated as well.

With continued reference to formula (1), in various embodiments at leastone of R¹, R², and R³ represent an organic radical, and in certainembodiments thereof each of R¹, R², and R³ represent an organic radical.In various preferred embodiments at least one of R¹, R² or R³ contains acarboxyl group.

For instance, in some embodiments at least one of R¹, R² and R³represent an organic radical selected from the group consisting of anoptionally substituted C₁-C₁₀ alkyl group, optionally substituted C₂-C₁₀alkenyl group, optionally substituted C₂-C₁₀ alkynyl group. As usedherein a “substituted group” is derived from the unsubstituted parentstructure in which there has been an exchange of one or more hydrogenatoms for another atom or group. In other embodiments at least one ofR¹, R² and R³ represent an organic radical selected from the groupconsisting of an optionally substituted C₄-C₁₀ cycloalkyl, optionallysubstituted C₄-C₁₀ cycloalkenyl, and optionally substituted 3-10membered heterocyclyl. In yet other embodiments at least one of R¹, R²and R³ represent an organic radical selected from the group consistingof an optionally substituted carbo- and heterocyclic 5-10 membered aryl.

In various embodiments the carboxylic acid is malonic acid, glutaricacid, methylsuccinic acid, or some combination thereof (e.g., malonicacid wherein, with reference to formula (1), R² and R³ represent H; andR¹ represents carboxyl group).

For a Li/Air cell, volatility of the active compound must be considered.Other than vapor pressure, boiling-point temperature and molecularweight have been found to provide a practical and useful metric formaking a first order approximation on the evaporative resistance of theactive compound whence dissolved. For instance, given similarstructures, compounds with higher molecular weights will have lowervolatility, and compounds with higher boiling points are generally lessvolatile. Of course low molecular weight acids are highly desirable fromthe perspective of energy density, but this singular approach to asuitable acid is ineffective for aqueous lithium air because it does notconsider evaporative losses over time.

To achieve an optimal, or near optimal, balance between the weight ofthe active compound and evaporative loss, polyprotic organic acids areproposed herein as the proton generating species. Because of theirrelatively moderate pKa values, these acids do not render the catholytepH so acidic as to destabilize the ion membrane or other cathodecompartment components such as but not limited to oxygenelectro-catalysts. Because organic polyprotic acids have at least twoacidic protons they can have a relatively high active proton capacityper unit of weight, and are generally robust enough in molecular weightto be sufficiently non-volatile for most or all applications, includingfor use in open to air cells. Preferably the boiling point of thecathode active materials is greater than 125° C., and even morepreferably the vapor pressure of the cathode active materials atstandard temperature and pressure is less than approximately 4-5 mmHg.In various embodiments the active proton generator is an organic acidsubstantially stable against evaporative losses, for example having avapor pressure lower than that of acetic acid (11.4 mmHg (20° C.)), inparticular much lower, such as less than 1 mmHg or less than 10⁻³ mmHg,for example malonic acid (3.2×10⁵ mmHg (25° C.)) or citric Acid(1.66×10⁻⁸ mmHg (25° C.)) For example, one particularly suitable organicpolyprotic acid is malonic acid.

The electrochemical reaction in a Li/Air cell incorporating a catholytecomprising malonic acid is a two-step process, one for each of the firstand second acidic protons, as illustrated below.

-   -   Anode: Li-e⁻        Li⁺    -   Cathode: 1) 4 Li⁺+4 HOOC—CH₂—COOH+O₂+4e⁻        4 LiOOC—CH₂—COOH+2H₂O        -   2) 4 Li⁺+4 LiOOC—CH₂—COOH+O₂+4e⁻            4 LiOOC—CH₂—COOLi+2H₂O

In addition to malonic acid, other particularly suitable polyproticacids are glutaric acid, methylsuccinic acid, and citric acid.

Accordingly, in various embodiments of the instant invention the aqueouscatholyte is acidic and comprises an active organic polyprotic acidcomprising organic radicalat least two acidic proton (e.g., three). Theutility of employing such an acid is at least two fold.

Firstly, polyprotic acids have the capacity to furnish more than onehydrogen ion per acid molecule, thus polyprotic acids can effectuategreater discharge capacity per unit weight in the acidic regime thanthat of a monoprotic acid of equal molecular weight. And from theperspective of volatility, polyprotic acids provide resistance toevaporative losses due to their molecular weight and relatively greaternumber of hydrogen bonds, but do not over burden the weight of the cellbecause they donate two or more active protons per acid molecule.Accordingly, polyprotic acids provide significant advantage when used inthe instant catholytes because the molecules are large enough to resistevaporative losses and do not significantly burden cell weight becauseof their large active proton to weight ratio. In various embodiments theactive proton to molecular weight ratio of the polyprotic organic activecompounds are preferably in the range of: 50-70 g/equivalent of H+;71-90 g/equivalent of H+; 91-110 g/equivalent of H⁺.

Secondly, the acid strength of polyprotic acids, because they comprisetwo or more acidic protons each characterized with corresponding pKavalue, may be tuned via partial neutralization to yield a catholyte ofdesired pH or one within a desired pH range. In some embodiments partialneutralization of the organic polyprotic acid yields an acid salt (e.g.,a lithium acid salt) wherein one or more, but not all, of the acidicprotons of the acid is neutralized by strong base to form water, and assuch the neutralized hydrogens are de-activated (i.e., no longeravailable as an active proton to participate in the cell reaction). Inother embodiments polyprotic acid yields an aminium neutral or acid saltwhere the number of acidic protons doesn't change as compared to theinitial acid. However, the formed aminium salt of a polyprotic organicacid has different pKa values, for instance raised, thus reducing theacid strength of the initial polyprotic organic acid.

H_(n)A+mR¹R²R³N:→[mR¹R²R³NH]⁺H_((n-m))A⁻,pKa₁(H_(n)A)<pKa([R¹R²R³NH]⁺)

where H_(n)A is polyprotic acid, n is number of acidic protons, R¹R²R³N:is an amine having a lone electron pair on nitrogen atom, R¹, R², R³ mayrepresent hydrogen, and at least one of them represents an aliphatic oraromatic optionally substituted organic radical. If m=n, the aminiumsalt is a neutral aminium salt.Accordingly, in various embodiments the catholyte comprises, prior toinitial discharge (or initial active operation) a neutral aminium saltin which all the acidic protons were transferred to amine molecules orto acid aminium salt containing one or more acidic protons in acidresidue.

The acid may be partially neutralized by adding a certain amount of abase to the dissolved polyprotic acid. By use of the term partialneutralization it is meant that the neutralization is not complete,which is to mean that one but not all of the acidic protons areneutralized in the process. For instance, for a triprotic acid the firstand/or second acidic hydrogen may be neutralized but not the third. Invarious embodiments the neutralizing agent is a strong base, such as ahydroxide, and preferably a hydroxide of the alkali metal. For instance,for a Li/Air cell the neutralizing agent may be LiOH.

In various embodiments once partially neutralized the polyprotic acid isconverted to an acid salt. For instance, partial neutralization ofmalonic acid by LiOH yields the acid salt lithium hydrogen malonate, orfor citric acid, the acid salt is lithium dihydrogen citrate ordilithium hydrogen citrate. In various embodiments the catholyte mayinclude both the organic polyprotic acid and its partially neutralizedcounterpart in various ratios, for example, the catholyte comprisingboth malonic acid and lithium hydrogen malonate. Preferably the lithiumacid salt is soluble in water and more preferably has solubility greaterthan 1 molar.

In various embodiments decreasing acid strength may be realized byadding a weak Lewis base having an atom with a lone electron pair thatreacts with the polyprotic acid to form an onium salt, and moreparticular aminium salt wherein one or more of the acidic protonsoriginally attached to the polyprotic acid are transferred to one ormore weak Lewis base molecules. By this expedient, the pKa values of theaminium salt are higher, and there is no loss of active proton capacitysince the acidic proton is merely transferred as opposed to beingneutralized. Preferably, the aminium salt is soluble in water and morepreferably has solubility greater than 1 molar. One particularlysuitable proton acceptor (i.e., weak Lewis base) is imidazole, and theresulting aminium salt isimidazolium malonate, or imidazolium hydrogenmalonate, or imidazolium citrate, or imidazolium hydrogen citrate, orimidazolium dihydrogen citrate.

In various embodiments the aforementioned polyprotic acids and aminiumsalts may be functionalized or substituted to enhance one or more of thefollowing characteristics: stability to oxidation, acid strength,resistance to evaporative losses, hygoscopicity of the acid or an acidsalt that forms as a result of cell discharge, as well as improvedoxidative stability of the acid residue.

For instance, in various embodiments the aqueous acidic catholyte of theinstant invention comprises water and, dissolved therein, a“functionally substituted” carboxylic acid for instance an amino acid orhydroxy acid.

In various embodiments the functionally substituted carboxylic acid isan amino acid, such as that containing an amine group, a carboxylicgroup, and an aliphatic or aromatic organic radical. In embodiments theamino acid has the following general formula

wherein R represents an aliphatic or aromatic optionally substitutedorganic divalent radical.

Amino acids and the like are advantageous because they may be used inthe form of an aminium salt where besides protonated amino group orgroups, it also has the acidic proton on carboxylic group. In the caseof such aminium salt, the molecular mass/active proton ratio canincrease. For instance, as illustrated below, an amino acid aminium saltconsumes two moles of alkali per one mole of amino acid aminium salt.

wherein X may be NO₃ ⁻, SO₄ ²⁻, ClO₄ ⁻

Suitable amino acids include Glycine, alanine, valine, proline,hydroxyproline, histidine, cysteine, serine, glutamine, lysine,hydroxylysine, arginine, methionine, asparagine, phenylalanine, andaminomalonic acid. For example glycine, alanine, and proline.

In various embodiments the functionally substituted carboxylic acid isan hydroxy acid such as that containing an hydroxy group, a carboxylicgroup, and an aliphatic or aromatic organic radical. In embodiments thehydroxy acid has the following general formula

wherein R represents an aliphatic or aromatic organic divalent radical.Suitable hydroxy carboxylic acids include citric acid, glycolic acid,lactic acid, 2-hydroxypropionic acid, 3-hydroxypropionic acid,2-hydroxybutyric acid, 3-hydroxybutyric acid, and the like (e.g., citricacid).

For example, citric acid may be the active compound, and the subsequentelectrochemical reaction of the cell may be represented by the followingequations

-   -   Anode: Li-e⁻        Li    -   Cathode: 1) 4 Li⁺+4 H₃C₆H₅O₇+O₂+4e⁻        4 LiH₂C₆H₅O₇+2H₂O        -   2) 4 Li⁺+4 LiH₂C₆H₅O₇+O₂+4e⁻            4 Li₂HC₆H₅O₇+2H₂O        -   3) 4 Li⁺+4 Li₂HC₆H₅O₇+O₂+4e⁻            4 Li₃C₆H₅O₇+2H₂O

Another particularly suitable class of molecule for use as an activecompound in the instant aqueous catholyte is phenols. Phenols areorganic compounds containing a hydroxyl group directly attached to anaromatic carbon atom, and may be represented by the general formula

Wherein R¹, R², R³, R⁴, R⁵=H, OH, CH₃, C₂H₅, C₃H₇, NH₂, NO₂, CN, COOH,SO₃H, C(R)═O, F, Cl, Br, I, CF₃, NR₃ ⁺, COOR, CONH₂, CCl₃, OR, NR₂; andR represents H, or an aliphatic or aromatic organic radical.

Phenol acidity and electrooxidation potential both depend on itssubstituents. The oxidation potential of substituted phenols becomesmore positive, and pK_(a) values become smaller, with an increase ofHammett's constant value. In other words, the direct electrochemicaloxidation of substituted phenol with an electron-withdrawing group ismore difficult, and acidity is higher than that of substituted phenolhaving an electron-donating group.

Particularly suitable phenols include resorcinol, 2-methylresorcinol,gallic acid, 4-nitrocathecol, 4-hydroxybenzoic acid, 2-nitroresorcinol;for example, a-resorcylic acid, a-resorcylonitrile.

In yet other embodiments the cathode active materials may besulfur-containing.

In various embodiments the aqueous catholyte of the instant inventioncomprises water and, dissolved therein, a sulfur-containing organiccompound such as sulfonic acid or an amide of sulfonic acid (i.e., asulfonamide). For instance, a sulfonic acid represented by the generalformula

wherein R represents an organic aliphatic or aromatic group.Or sulfonamides represented by the general formula

wherein R¹, R²=organic aliphatic or aromatic group.

Suitable suflonic acids include MES (2-(N-Morpholino)ethanesulfonicacid), MOPS (3-(N-Morpholino)propanesulfonic acid), BES(N,N-Bis(2-hydroxyethyl)-2-aminoethanesulfonic acid), TES(2-[(2-Hydroxy-1,1-bis(hydroxymethyl) ethyl)amino]ethanesulfonic acid),TAPSO (2-Hydroxy-3-[tris(hydroxymethyl)methylamino]-1-propanesulfonicacid, N-[Tris(hydroxymethyl) methyl]-3-amino-2-hydroxypropanesulfonicacid), HEPPS (4-(2-Hydroxyethyl)-1-piperazinepropanesulfonic acid), CHES(2-(Cyclohexylamino) ethanesulfonic acid), 3-Aminobenzenesulfonic acid;for example MES, MOPS, and HEPPS.

Suitable sulfonamides include o-, m-, p-aminobenzenesulfonamides, o-,m-, p-methylbenzenesulfonamides, o-, m-, p-cyanobenzenesulfonamides,4,4′-diaminobenzenesulphanilide.

Still in other embodiments the cathode active material is anitrogen-containing salt.

Accordingly, in various embodiments the aqueous catholyte of the instantinvention comprises water and, dissolved therein, an aminium salt formedwith inorganic acid. For instance, a salt represented by the followinggeneral formula (HNR¹R²R³)⁺X⁻, wherein X⁻ represents an inorganic acidresidue, and R¹, R², R³ may represent hydrogen, and at least one of themrepresents an aliphatic or aromatic optionally substituted organicradical. The aminium salt is preferably a nitrate.

Particularly suitable such salts include aniline nitrate,diethylenetriamine nitrate, ethanolamine nitrate, 2-methyl-1-pyrrolinenitrate, methoxyamine nitrate, N-methoxymethylamine nitrate,1-benzoylpiperazine nitrate, N-methylhydroxylamine nitrate,2-aminocyanopropane nitrate, N,N-diethylcyanoacetamide nitrate,2,2-diethylaminopropionitrile nitrate, 2-amino-2-cyanoproapne,dimethylamniacetonitrile nitrate, piperazine dinitrate,N,N-dimethylethylenediamine dinitrate, N-ethylmorpholine nitrate, andtriethanolamine nitrate.

Alternatively, the aminium cation of the salt may be based on aN-heterocyclic aliphatic or aromatic compound, such as imidazole.Particularly suitable such salts include imidazolium nitrate,2-methylimidazolium nitrate, 4-hydroxymethyl imidazolium nitrate,4-hydroxybenzimidazolium nitrate, 4-methoxybenzimidazolium nitrate,4-(N-methylacetamido)pyridinium nitrate, o-, m-, p-methylpyridiniumnitrate, o-, m-, p-ethylpyridinium nitrate, 2-methoxypyridinium nitrate,3-methoxypyridinium nitrate, 3-hydroxypyridinium nitrate,4-hydroxypyridinium nitrate, 3-fluoropyridinium nitrate,3-bromopyridinium nitrate, 3-sulfoxypyridinium nitrate,3-aminopyridazinium nitrate, 3-carboxypyridinium nitrate,4-methoxypyridazinium nitrate, and 2-amino-4,6-dimethyl pyraziniumnitrate; for example, imidazolium nitrate.

In accordance with the various preceding embodiments, substitutionand/or functionalization of the parent structure of the active compound,such as that represented in formula (1) and the like, can be used totune the acid strength of the compound.

In another aspect of the invention, the catholyte 6 comprises an activeagent that, rather than donating an acidic proton into the catholyte viaacid dissociation, effectively buffers the catholyte via reaction ofalkaline hydrolysis with the cell discharge product (lithium hydroxide).Preferably the alkaline hydrolysis reaction is reversible, thusproviding benefit to either primary or secondary Li/Air batteries.

Particularly suitable agents are carboxylic acid derivatives includingacyl halides, anhydrides, esters, amides and nitriles; especiallyesters, including diethylene glycol dibenzoate, 2-methoxyethylcyanoacetate, ethylene glycol monosalicylate, and ethylene brassylate.For instance, in embodiments wherein the agent is a carboxylic acidderivative, the cell reaction may be generalized as follows.

Li⁺+R(COX)_(n)+¼O₂+½H₂O+e→RCOOLi(COX)_(n-1)+XH

Li⁺+RCOOLi(COX)_(n1)+¼O₂+½H₂O+e→R(COOLi)₂(COX)_(n-2)+XH

. . .

Li⁺+R(COOLi)_(n-1)COX+¼O₂+½H₂O+e→R(COOLi)_(n)+XH

Li⁺+¼O₂+½H₂O+e→LiOH

-   -   where R is multivalent organic radical with 1 to 10 carbon        atoms;    -   n=1-5

In various use applications stability of the ion conductive membrane incontact with the catholyte is essential, and the extent of thatstability can be determinative of battery service life. Withoutintending to be limited by theory or any particular mechanism ofmembrane degradation, in aqueous solution ion exchange at the surfacecan lead to impedance rise that may ultimately cause pre-maturepolarization of the cell and early failure. In one aspect the presentinvention provides aqueous catholytes that enhance the stability of themembrane by incorporating in the catholyte an amount of lithium saltsufficient to suppress ion exchange, and, in addition, said salts arepreferably hygroscopic and assist in water management to prevent celldry out due to evaporative water loss which can occur over time in anopen to air cell.

In an open to air cell (e.g., Li/Air cell) the anion composition of thesupporting salt must be considered as it pertains to electrochemicalstability on charge, and in particular stability against anodicoxidation in order to avoid undesirable reactions, such as the formationof a volatile toxic compound. For that reason alone chloride salts,while suitable for use in a primary lithium air battery cell, andgenerally considered to be highly innocuous and safe since they aretypically known in the chemical fields as spectator ions, are in variousembodiments entirely unsuitable herein as a salt in a secondary aqueouslithium air battery if upon charge chloride gas forms prior to theoxygen evolution reaction (i.e., OER). Accordingly, in variousembodiments of the instant invention the catholyte is devoid of anychloride containing salts, and even more preferably devoid of freechloride ions in the catholyte. Preferably the anion of the supportingsalt is NO₃ ⁻, ⁻SO₄ ²⁻, or ClO₄ ⁻, for example nitrate.

In various embodiments the supporting salt concentration in thecatholyte is about 1 molar or about 2 molar and typically greater than 1molar. Preferably the salt is lithium nitrate.

In the various preceding embodiments the supporting lithium salts andlithium salts that are produced as a result of cell discharge arepreferably soluble in water, hygroscopic and have water solubilitygreater than 1 molar (i.e., are soluble in water to concentrationsgreater than 1 molar).

To increase service life of a Li/Air battery cell the acid generatingactive compound, regardless of the manner in which the cell is operated,is most preferably non-volatile. By use of the term substantiallynon-volatile it is meant that the acid has a sufficiently low vaporpressure and that the molecules of the compound, whence dissolved in thecatholyte, are not evaporated out of the cell to an extent that wouldcause the cell to lose more than 10% of the active compound over theoperating service life of the cell, wherein the operating service lifebegins when the catholyte is exposed to ambient air, such as uponactivation (e.g., by peeling a release layer off of the gas entryholes). More preferably the evaporative loss is less than 5%, and evenmore preferably less than 2% over the operating service life. Inpreferred embodiments the vapor pressure of the acid generating speciesand its lithium salt is less than 11 mmHg at standard temperature andpressure, in particular embodiments orders of magnitude less, and/or theboiling point temperature is greater than 125° C.

In the various preceding embodiments the anodic oxidative stability ofthe active compound or agent may be enhanced to achieve more effectivecycling, and in particular this may be accomplished through substitutionor addition of organic radicals, functional groups or other groups thatare electron withdrawing or otherwise increase the anodic oxidationpotential of the active compound, or in the case of an acid, itsconjugate base. Preferably, the potential of electro-oxidation isgreater than the oxygen evolution potential for the initial compositionof the aqueous catholyte, and its products of discharge.

For example, the addition of an electron withdrawing group to the acidmolecule through substitution or otherwise can provide benefit as itpertains to the electro-oxidative stability of the acid, and inparticular its conjugate base. Electro-oxidative stability is of courseimportant for a rechargeable Li/O₂ battery cell, and electronwithdrawing groups such as halogens, halogenated organic groups, cyano,nitro, sulfo, and carboxyl groups may be attached to the acid toincrease its anodic oxidation potential above that for the oxygenevolution reaction (OER), or to further stabilize the acid for thoseinstances wherein the potential of the OER increases over the course ofcell cycling; for example, via the loss of catalytic activity in thecathode.

In another aspect of the instant invention a Li/Air battery cell (ormore generally a Li/O₂ battery cell) is provided that may be dischargeddeeply into the basic regime with improved reversibility on charge byusing a third approach (or method) that encompasses discharging the cellinto the basic regime and charging the cell into the acidic regime, andin particular charging the cell beyond a capacity sufficient to renderthe pH of the catholyte sufficient to cause decomposition of lithiumcarbonate.

Said third approach involves starting with an acidic catholytecontaining an acid generating chemical species (or active compound) thathas the following requisite properties of substantial non-volatility,chemically compatibility in contact with the membrane, and stability toelectro-oxidation, which is to mean that during the charging cycle(whence molecular oxygen is formed and evolved from the cell catholyte)the conjugate base of the acid is not electro-oxidized. Moreover, the pHof the initial catholyte (i.e., the catholyte composition prior to theinitial discharge) should be sufficiently acidic to effectuatedecomposition of lithium carbonate during the charging cycle.

The instant method takes advantage of the fact that solid carbonates aresoluble and undergo acid base decomposition involving CO₂ (g) evolutionwhen placed in an acidic medium of sufficient acid strength. Forinstance, in accordance with the following sequence of reactions:

Li₂CO₃+HA→LiHCO₃+LiA  (1)

LiHCO₃+HA→H₂CO₃+LiA  (2)

H₂CO₃

H₂O+CO₂  (3)

In various embodiments the method involves: i) starting with an acidiccatholyte of sufficient acid strength to dissolve and react thecarbonate salt as described above; ii) discharging the cell from thisacidic state into the basic regime wherein LiOH may precipitate, and thecatholyte, now alkaline and exposed to ambient air, is susceptible tocarbonation and the formation of solid carbonate; and iii) charging thecell into the acidic regime, and to a sufficient capacity to render thepH of the catholyte acidic enough (i.e., of a low enough pH) to drivedissolution and decomposition of the lithium carbonate salt.

Provided that the catholyte is properly formulated as generally taughtabove and further described below using a more detailed embodiment, saidthird approach provides many advantages compared to cycling exclusivelyin the acidic regime (as is prescribed by the second approach), or thatof solely cycling in the basic regime or between neutral and basicregimes (which is the case for said first approach).

Foremost among the advantages of the third approach is the simultaneousimprovement in specific gravity and reversibility, which leads to higherenergy density and longer cycle life. The theoretical energy density ofcells cycled in both the acidic and basic regime can be twice that ofcells cycled exclusively in the acidic regime, and far more reversiblewhen compared to cycling cells within the neutral/basic regime. Theenergy density boost is derived from two factors. Firstly, capacity inthe acidic regime is derived from the acidic protons of the activecompound, and, secondly, water necessary to operate the cell in thebasic regime is furnished as a product of discharge in the acidicregime.

2Li+½O₂+2HA

2LiA+H₂O [acidic regime]

2Li+½O₂+H₂O

2LiOH [basic regime]

The improved reversibility stems from charging the cell into the acidicregime to a sufficiently low pH that solid lithium carbonate isdissolved and decomposed, and as a result the lithium capacity thatwould have otherwise been lost as an element trapped in the carbonate,is reversibly recovered on charge. By this expedient, reversiblesecondary Li/Air cells are provided having a theoretical energy densitythat is significantly larger than that of the same cell cycled solely inthe acidic regime, but with greatly improved reversibility when comparedto a cell that is operated exclusively in the basic regime.

Various charging protocols are contemplated herein to enhance the rateat which and the extent to which the catholyte may be regenerated duringthe charging cycle. These include holding the cell at constant voltageor at relatively low constant current whence the catholyte pH issufficiently acidic to stimulate acid decomposition of carbonate solidproducts, as described above. By use of the term regenerated whenreferring to the catholyte it is meant that lost lithium capacity can berecovered on charge. To effect regeneration the acid strength of theinitial catholyte (also sometimes referred to herein as the startingcatholyte) should be sufficient to decompose the carbonate but not soacidic as to degrade the membrane. For this purpose suitable pH valuesare typically in the range of about 2.5 to 4.5, preferably 3 to 4 andmore preferably 3.1 to 3.8, e.g., 3.5.

In an open to air cell, acid strength alone (i.e., pH of the catholyte)is not enough to stabilize prolonged cycling if the acid used to effectthe pH is itself volatile in air. Accordingly, for a Li/Air cell, theproton generating species that acidifies the catholyte is preferablyresistant to evaporative losses, and, moreover, the pH of the catholyteis preferably tuned by the composition of the active compound so as tonot degrade the solid electrolyte membrane, especially during initialstorage of the cell, wherein prolonged contact with the catholyte iscontemplated.

In various embodiments, the active compounds are entirely non-volatile.For instance, in various embodiments the active compound comprises metalaqua ions that interact with the product of cell discharge (hydroxideions); for example, zinc and magnesium ions. The metal ions may beincorporated in the cell by dissolution of an inorganic neutral saltderived from a strong acid and a weak base. The cell reaction may begeneralized by the following set of equations.

XLi⁺+M_(x)A_(y)+¼·XO₂+½·XH₂O+xe→[MOH]_(x)A_(y-1)+Li_(x)A

XLi⁺+[MOH]_(x)A_(y-1)+¼·XO₂+½·XH₂O+xe→[M(OH)₂]_(x)A_(y-2)+Li_(x)A

. . .

XLi⁺+[M(OH)_(y-1)]_(x)A+¼·XO₂+½·XH₂O+xe→M(OH)_(y)+Li_(x)A

Li⁺+¼O₂+½H₂O+e→LiOH

-   -   where M=metal; A=acid residue; x=basicity of an acid; y=metal        oxidation number

In particular magnesium nitrate:

Li⁺+Mg(NO₃)₂+¼O₂+½H₂O+e→Mg(OH)NO₃+LiNO₃

Li⁺+Mg(OH)NO₃+¼O₂+½H₂O+e→Mg(OH)₂+LiNO₃

Li+¼O₂+½H₂O+e→LiOH

Through judicious selection, the salt may also serve a secondarypurpose, albeit no less important for an open to air cell, which is tofacilitate water management and in particular to maintain a sufficientwater content in the catholyte to prevent dry out. Accordingly, it ispreferable to use an active salt that is also hygroscopic. For instance,particularly preferred anions (or acid residue as it sometimes referredto) include nitrate, sulfate and perchlorate. It is also equallyimportant that the acid residue be stable to electro-oxidation in orderto avoid undesirable reactions, such as the formation of a toxic gas oncharge. For that reason alone chloride salts, while suitable for use ina primary lithium air battery, and generally considered to be highlyinnocuous and safe since they are typically known in the chemical fieldsas spectator ions, are in various embodiments entirely unsuitable hereinas a salt in a secondary aqueous lithium air battery if upon chargechloride gas forms prior to the OER. Accordingly, in various embodimentsof the instant invention the catholyte is devoid of any chloridecontaining salts, and even more preferably devoid of free chlorine ionsin the catholyte.

In various embodiments tuning the acidity of the starting catholyte isguided by balancing at least the following two parameters: i) stabilityof the membrane in contact with the catholyte, and in particular thecatholyte should not be so acidic as to degrade membrane performance;and ii) decomposition of lithium carbonate, the reaction of whichrequires a certain acid strength in order to proceed. Preferably therange of pH of the starting catholyte and/or the pH of the catholytethat is reached during charge is greater than that value which woulddegrade the membrane but less than about pH 4, or 3.5 or 3. Theinventors have found that, when a lithium titanium phosphate solidelectrolyte membrane is utilized, the pH of the catholyte is preferablygreater than about 3, but should be preferably less than about 4 inorder to promote significant rates for catholyte regeneration on charge.

Catholyte tuning may be achieved using a mixture of two or moreinorganic salts. For example: i) 2.5 molar magnesium nitrate, 0.5 molarzinc nitrate, and 1 molar lithium nitrate; ii) 2.8 molar magnesiumnitrate, 0.2 molar zinc nitrate, and 1 molar lithium nitrate; iii) 2.95molar magnesium nitrate, 0.05 molar zinc nitrate, and 1 molar lithiumnitrate.

In particular embodiments the instant Li/O₂ battery cells comprise acatholyte having one of the following compositions:

-   -   i) 4 molar malonic acid and 2 molar lithium nitrate;    -   ii) 2 molar malonic acid, 2 molar lithium hydrogen malonate and        1 molar lithium nitrate;    -   iii) 1 molar malonic acid, 3 molar lithium hydrogen malonate and        1 molar lithium nitrate;    -   iv) 0.5 molar malonic acid, 1.5 molar lithium hydrogen malonate        and 1 molar lithium nitrate;    -   v) 4 molar imidazolium hydrogen malonate and 2 molar lithium        nitrate;    -   vi) 4 molar imidazolium hydrogen malonate and 1 molar lithium        nitrate;    -   vii) 2 molar citric acid and 2 molar lithium nitrate;    -   viii) 2 molar lithium dihydrogen citrate and 2 molar lithium        nitrate;    -   ix) 1 molar lithium dihydrogen citrate and 1 molar lithium        nitrate;    -   x) 2 molar imidazolium dihydrogen citrate and 2 or 1 molar        lithium nitrate;    -   xi) 2 molar imidazolium hydrogen citrate and 2 or 1 molar        lithium nitrate;    -   xii) 2.5 molar magnesium nitrate, 0.5 molar zinc nitrate and 1        molar lithium nitrate (pH about 3.1);    -   xiii) 2.8 molar magnesium nitrate, 0.2 molar zinc nitrate, and 1        molar lithium nitrate (pH about 3.5);    -   xiv) 2.95 molar magnesium nitrate and 0.05 molar zinc nitrate        and 1 molar lithium nitrate (pH about 3.8).

Other Cell Components

With reference to FIG. 1A, the cell comprises a Li anode 1. The anodemay be an alkali metal, alloy or intercalation material, for example Limetal or a Li metal alloy or Li intercalation material (e.g., lithiatedcarbon). In one example, a Li metal foil may be used. Lithium anodes,including intercalation anodes and lithium alloys and lithium metalanodes are well known in the lithium battery art. In preferredembodiments the anode is lithium metal (e.g., in foil or sintered form)and of sufficient thickness (i.e., capacity) to enable the cell toachieve the rated discharge capacity of the cell. The anode may take onany suitable form or construct including a green or sintered compact(such as a wafer or pellet), a sheet, film, or foil, and the anode maybe porous or dense. Without limitation, the lithium anode may have acurrent collector (e.g., copper foil, or suitable expandable metal)pressed or otherwise attached to it in order to enhance the passage ofelectrons between it and the leads of the cell. Without limitation thecell may be anode or cathode limited. When anode limited, the completedischarge (corresponding to rated capacity) will substantially exhaustall the lithium in the anode. When cathode limited, some active lithiumwill remain subsequent to the cell delivering its rated capacity.

The anode is protected with a protective membrane architecturechemically stable to both the anode and the environment of an adjacentcathode compartment (4). The protective membrane architecture typicallycomprises a solid electrolyte protective membrane 2 and an interlayer 3.The solid electrolyte protective membrane is sometimes referred toherein as an ion membrane or a liquid impermeable alkali metal ionconductive solid electrolyte barrier layer. The protective membranearchitecture is in ionic continuity with the Li anode 1 and isconfigured to selectively transport Li ions into and out of the cathodecompartment 4 while providing an impervious barrier to the environmentexternal to the anode. Protective membrane architectures suitable foruse in the present invention are described in applicants' co-pendingpublished US Applications US 2004/0197641 and US 2005/0175894 and theircorresponding International Patent Applications WO 2005/038953 and WO2005/083829, respectively, incorporated by reference herein.

With reference to FIG. 1B, there is illustrated (in cross-section (left)and perspective (right)) an embodiment of a lithium air battery cell 10in accordance with the instant invention. The cell is disposed in a case11 (e.g., a metal or polymeric case, including but limited to a heatsealable multilayer laminate used for that purpose). The case comprisesone or more ports 12 for the passage of oxygen and moisture from theambient air. To effectively reach the cathode and the cathodecompartment, as illustrated in FIG. 1B, the case side wall of whichcontains the ports is adjacent to the cathode.

In many, but not necessarily all embodiments, the cell is activated byremoving a barrier material (not shown) which covers the ports toprevent, prior to cell activation, premature or excessive exposure ofthe cathode compartment to ambient air. The cell activated by removingthe barrier material (e.g., by the act of peeling off a tab (barriermaterial layer).

The case may further comprise an additional port (not shown) forintroducing, water or catholyte into the cathode compartment after thecell has been manufactured. Without limitation, the catholyte (or water)may be introduced, prior or subsequent to one or more of the following:cell activation or initial discharge. For instance, the cell may be usedin a Li/Air, or more specifically, a Li/O₂ flow battery, wherein thecatholyte is caused to flow into, and generally through, the cathodecompartment. In accordance with such embodiments the battery may containappropriate pipeworks and pumps for circulating the catholyte may bestored external from the cell in, e.g., a suitable storage container.

FIGS. 2A-D illustrate representative protective membrane architecturesfrom these disclosures suitable for use in the present invention. Theprotective membrane architectures provide a barrier to isolate a Lianode from ambient and/or the cathode side of the cell while allowingfor efficient ion Li metal ion transport into and out of the anode. Thearchitecture may take on several forms. Generally it comprises a solidelectrolyte layer that is substantially impervious, ionically conductiveand chemically compatible with the external ambient (e.g., air or water)or the cathode environment.

Referring to FIG. 2A, the protective membrane architecture can be amonolithic solid electrolyte 202 that provides ionic transport and ischemically stable to both the alkali metal anode 201 and the externalenvironment. Examples of such materials are Na-β” alumina, LiHfPO₄ andNASICON, Nasiglass, LisLa₃Ta₂O₁₂ and Li₅La₃Nb₂O₁₂. Na₅MSi₄O₁₂ (M: rareearth such as Nd, Dy, Gd).

More commonly, the ion membrane architecture is a composite composed ofat least two components of different materials having different chemicalcompatibility requirements, one chemically compatible with the anode,the other chemically compatible with the exterior; generally ambient airor water, and/or battery electrolytes/catholytes. By “chemicalcompatibility” (or “chemically compatible”) it is meant that thereferenced material does not react to form a product that is deleteriousto battery cell operation when contacted with one or more otherreferenced battery cell components or manufacturing, handling, storageor external environmental conditions. The properties of different ionicconductors are combined in a composite material that has the desiredproperties of high overall ionic conductivity and chemical stabilitytowards the anode, the cathode and ambient conditions encountered inbattery manufacturing. The composite is capable of protecting an alkalimetal anode from deleterious reaction with other battery components orambient conditions while providing a high level of ionic conductivity tofacilitate manufacture and/or enhance performance of a battery cell inwhich the composite is incorporated.

Referring to FIG. 2B, the protective membrane architecture can be acomposite solid electrolyte 210 composed of discrete layers, whereby thefirst material layer 212 (also sometimes referred to herein as“interlayer”) is stable to the alkali metal anode 201 and the secondmaterial layer 214 is stable to the external environment. Alternatively,referring to FIG. 2C, the protective membrane architecture can be acomposite solid electrolyte 220 composed of the same materials, but witha graded transition between the materials rather than discrete layers.

Generally, the solid state composite protective membrane architectures(described with reference to FIGS. 2B and C) have a first and secondmaterial layer. The first material layer (or first layer material) ofthe composite is ionically conductive, and chemically compatible with analkali metal electrode material. Chemical compatibility in this aspectof the invention refers both to a material that is chemically stable andtherefore substantially unreactive when contacted with an alkali metalelectrode material. It may also refer to a material that is chemicallystable with air, to facilitate storage and handling, and reactive whencontacted with an alkali metal electrode material to produce a productthat is chemically stable against the alkali metal electrode materialand has the desirable ionic conductivity (i.e., a first layer material).Such a reactive material is sometimes referred to as a “precursor”material. The second material layer of the composite is substantiallyimpervious, ionically conductive and chemically compatible with thefirst material. Additional layers are possible to achieve these aims, orotherwise enhance electrode stability or performance. All layers of thecomposite have high ionic specific conductivity, at least 10⁻⁷ S/cm,generally at least 10⁻⁶ S/cm, for example at least 10⁻⁵ S/cm to 10⁻⁴S/cm, and as high as 10⁻³ S/cm or higher so that the overall ionicconductivity of the multi-layer protective structure is at least 10⁻⁷S/cm and as high as 10⁻³ S/cm or higher.

A fourth suitable protective membrane architecture is illustrated inFIG. 2D. This architecture is a composite 230 composed of an interlayer232 between the solid electrolyte 234 and the alkali metal anode 201whereby the interlayer includes a liquid or gel phase anolyte. Thus, thearchitecture includes an alkali metal ion conducting separator layerwith a non-aqueous anolyte (i.e., electrolyte about the anode), theseparator layer being chemically compatible with the alkali metal and incontact with the anode; and a solid electrolyte layer that issubstantially impervious (pinhole- and crack-free) ionically conductivelayer chemically compatible with the separator layer and aqueousenvironments and in contact with the separator layer. The solidelectrolyte layer of this architecture (FIG. 2D) generally shares theproperties of the second material layer for the composite solid statearchitectures (FIGS. 2B and C). Accordingly, the solid electrolyte layerof all three of these architectures will be referred to below as asecond material layer or second layer.

A wide variety of materials may be used in fabricating protectivecomposites in accordance with the present invention, consistent with theprinciples described above. For example, in the solid state embodimentsof Figs. B and C, the first layer (material component), in contact withthe alkali metal, may be composed, in whole or in part, of alkali metalnitrides, alkali metal phosphides, alkali metal halides alkali metalsulfides, alkali metal phosphorous sulfides, or alkali metal phosphorusoxynitride-based glass. Specific examples include Li₃N, Li₃P, LiI, LiBr,LiCl, LiF, Li₂S—P₂S₅, Li₂S—P₂S₅—LiI and LiPON. Alkali metal electrodematerials (e.g., lithium) may be applied to these materials, or they maybe formed in situ by contacting precursors such as metal nitrides, metalphosphides, metal halides, red phosphorus, iodine, nitrogen orphosphorus containing organics and polymers, and the like with lithium.A particularly suitable precursor material is copper nitride (e.g.,Cu₃N). The in situ formation of the first layer may result from anincomplete conversion of the precursors to their lithiated analog.Nevertheless, such incomplete conversions meet the requirements of afirst layer material for a protective composite in accordance with thepresent invention and are therefore within the scope of the invention.

For the anolyte interlayer composite protective architecture embodiment(FIG. 2D), the protective membrane architecture has an alkali metal ionconducting separator layer chemically compatible with the alkali metalof the anode and in contact with the anode, the separator layercomprising a non-aqueous anolyte, and a substantially impervious,ionically conductive layer (“second” layer) in contact with theseparator layer, and chemically compatible with the separator layer andwith the exterior of the anode. The separator layer can be composed of asemi-permeable membrane impregnated with or otherwise including anorganic anolyte. For example, the semi-permeable membrane may be amicro-porous polymer, such as are available from Celgard, Inc. Theorganic anolyte may be in the liquid or gel phase. For example, theanolyte may include a solvent selected from the group consisting oforganic carbonates, ethers, lactones, sulfones, etc, and combinationsthereof, such as EC, PC, DEC, DMC, EMC, 1,2-DME or higher glymes, THF,2MeTHF, sulfolane, and combinations thereof. 1,3-dioxolane may also beused as an anolyte solvent, particularly but not necessarily when usedto enhance the safety of a cell incorporating the structure. When theanolyte is in the gel phase, gelling agents such as polyvinylidinefluoride (PVdF) compounds, hexafluropropylene-vinylidene fluoridecopolymers (PVdf-HFP), polyacrylonitrile compounds, cross-linkedpolyether compounds, polyalkylene oxide compounds, polyethylene oxidecompounds, and combinations and the like may be added to gel thesolvents. Suitable anolytes will, of course, also include alkali metalsalts, such as, in the case of lithium, for example, LiPF₆, LiBF₄,LiAsF₆, LiSO₃CF₃ or LiN(SO₂C₂F₅)₂. In the case of sodium, suitableanolytes will include alkali metal salts such as NaClO₄, NaPF₆, NaAsF₆NaBF₄, NaSO₃CF₃, NaN(CF₃SO₂)₂ or NaN(SO₂C₂F₅)₂, One example of asuitable separator layer is 1 M LiPF₆ dissolved in propylene carbonateand impregnated in a Celgard microporous polymer membrane.

The second layer (material component) of the protective composite may becomposed of a material that is substantially impervious, ionicallyconductive and chemically compatible with the first material orprecursor, including glassy or amorphous metal ion conductors, such as aphosphorus-based glass, oxide-based glass, phosphorus-oxynitride-basedglass, sulfur-based glass, oxide/sulfide based glass, selenide basedglass, gallium based glass, germanium-based glass, Nasiglass; ceramicalkali metal ion conductors, such as lithium beta-alumina, sodiumbeta-alumina, Li superionic conductor (LISICON), Na superionic conductor(NASICON), and the like; or glass-ceramic alkali metal ion conductors.Specific examples include LiPON, Li₃PO₄.Li₂S.SiS₂, Li₂S.GeS₂.Ga₂S₃,Li₂O.11Al₂O₃, Na₂O.11Al₂O₃, (Na,Li)_(1+x)Ti_(2-x)Al_(x)(PO₄)₃(0.1≦x≦0.9) and crystallographically related structures,Li_(1+x)Hf_(2-x)Al_(x)(PO₄)₃ (0.1≦x≦0.9), Na₃Zr₂Si₂PO₁₂, Li₃Zr₂Si₂PO₁₂,Na₅ZrP₃O₁₂, Na₅TiP₃O₁₂, Na₃Fe₂P₃O₁₂, Na₄NbP₃O₁₂, Na- Silicates,Li_(0.3)La_(0.5)TiO₃, Na₅MSi₄O₁₂ (M: rare earth such as Nd, Gd, Dy)Li₅ZrP₃O₁₂, Li₅TiP₃O₁₂, Li₃Fe₂P₃O₁₂ and Li₄NbP₃O₁₂, and combinationsthereof, optionally sintered or melted. Suitable ceramic ion alkalimetal ion conductors are described, for example, in U.S. Pat. No.4,985,317 to Adachi et al., incorporated by reference herein in itsentirety and for all purposes.

A particularly suitable glass-ceramic material for the second layer ofthe protective composite is a lithium ion conductive glass-ceramichaving the following composition:

Composition mol % P₂O₅ 26-55%  SiO₂ 0-15% GeO₂ + TiO₂ 25-50%  in whichGeO₂ 0-50% TiO₂ 0-50% ZrO₂ 0-10% M₂O₃ 0-10% Al₂O₃ 0-15% Ga₂O₃ 0-15% Li₂O3-25%

and containing a predominant crystalline phase composed ofLi_(1+x)(M,Al,Ga)_(x)(Ge_(1-y)Ti_(y))_(2-x)(PO₄)₃ where X≦0.8 and0≦Y≦1.0, and where M is an element selected from the group consisting ofNd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb and/orLi_(1+x+y)Q_(x)Ti_(2-x)Si_(y)P_(3-y)O₁₂ where 0<X≦0.4 and 0<Y≦0.6, andwhere Q is Al or Ga. The glass-ceramics are obtained by melting rawmaterials to a melt, casting the melt to a glass and subjecting theglass to a heat treatment. Such materials are available from OHARACorporation, Japan and are further described in U.S. Pat. Nos.5,702,995, 6,030,909, 6,315,881 and 6,485,622, incorporated herein byreference.

Another particularly suitable material for the second layer of theprotective composite are lithium ion conducting oxides having a garnetlike structures. These include Li₆BaLa₂Ta₂O₁₂; Li₇La₃Zr₂O₁₂,Li₅La₃Nb₂O₁₂, Li₅La₃M₂O₁₂ (M=Nb, Ta)Li_(7+x)A_(x)La_(3-x)Zr₂O₁₂ where Amay be Zn. These materials and methods for making them are described inU.S. Patent Application Pub. No.: 2007/0148533 (application Ser. No.10/591,714) and is hereby incorporated by reference in its entirety andsuitable garnet like structures, are described in International PatentApplication Pub. No.: WO/2009/003695 which is hereby incorporated byreference for all that it contains.

The composite should have an inherently high ionic conductivity. Ingeneral, the ionic conductivity of the composite is at least 10⁻⁷ S/cm,generally at least about 10⁻⁶ to 10⁻⁵ S/cm, and may be as high as 10⁻⁴to 10⁻³ S/cm or higher. The thickness of the first precursor materiallayer should be enough to prevent contact between the second materiallayer and adjacent materials or layers, in particular, the alkali metalof the anode. For example, the first material layer for the solid statemembranes can have a thickness of about 0.1 to 5 microns; 0.2 to 1micron; or about 0.25 micron. Suitable thickness for the anolyteinterlayer of the fourth embodiment range from 5 microns to 50 microns,for example a typical thickness of Celgard is 25 microns.

The thickness of the second material layer is preferably about 0.1 to1000 microns, or, where the ionic conductivity of the second materiallayer is about 10⁻⁷ S/cm, about 0.25 to 1 micron, or, where the ionicconductivity of the second material layer is between about 10⁻⁴ about10⁻³ S/cm, about 10 to 1000 microns, preferably between 1 and 500microns, and more preferably between 10 and 100 microns, for exampleabout 20 microns.

Seals and methods of making seals which are particularly suitable forsealing protected anodes described hereinabove and elsewhere, includingcompliant and rigid seals, are fully described in US Patent ApplicationNo.: 2007/0037058 and US Patent Application No.: US 2007/0051620 toVisco et al., and are hereby incorporated by reference in theirentirety, particularly for their description of battery cell sealarchitectures.

Cathode Compartment

Referring again to FIG. 1A, the cathode compartment 4 comprises an aircathode 5 (also sometimes referred to herein as “oxygen electrode”) andan aqueous catholyte 6, which is disposed between the cathode 5 and thesolid electrolyte protective membrane 2 and is in direct contact withthe cathode 5 for reducing molecular oxygen. The cathode compartment 4can further comprise one or more porous solid reservoir structures 7disposed between the solid electrolyte protective membrane 2 and the aircathode 5. The aqueous catholyte 6 and porous solid reservoir 7 arerepresented as separate layers in FIG. 1A for ease of illustration,however they may be and often are co-extensive in many embodiments ofthe invention.

Reservoir Structures

It has been found that several types of porous structures can beeffectively used as reservoir layers in Li/air aqueous cells inaccordance with the present invention. These porous layers arechemically inert and compatible with the cathode and with the aqueouscatholyte. In particular, they do not react with the catholytecomponents, cannot be oxidized by the cathode, and do not participate inthe cell discharge as reagents. The first function of a porous reservoirdisposed between the cathode and the protective membrane is that itshould be loaded with the aqueous catholytes and/or solid phase activecompounds or active agents as described above. Solid structure(s) usedas reservoir layer(s) have high porosity. It has also been found thatreservoir layers can have a second function of accommodating both liquidand solid cell discharge products, thereby increasing the depth ofdischarge and improving cell characteristics. Additionally, the porousspace of the reservoir layer retains water that is absorbed by thehygroscopic components of the catholyte during cell discharge andstorage thereby making it available for discharge reactions.

Porous reservoir structures suitable for use herein are describedelsewhere and will not be repeated herein but are fully described U.SPatent Publication No. US 2009/0311596, hereby incorporated by referencein its entirety. As described in detail in the aforementioned reference,suitable porous reservoir structures include, but are not limited to thefollowing: metal oxides (e.g., porous ZrO₂), in particular, Zirconiacloth from Zircar Products, Inc.); carbonaceous porous reservoirs,including carbon and graphite cloths and felts, carbon papers; e.g., WDFgraphite felt and VDG carbon felt from National Electric CarbonProducts, Inc. and carbon felt from Fiber Materials, Inc. can be used;polymeric porous reservoirs such as polymeric layers with high porosity(e.g., at least 50%, for example 90%) can be used as reservoirstructures, an example of such a reservoir is polypropylene fibermaterials; hydrogels are also suitable reservoir layers, typically theseare hydrophilic polymer networks that can absorb water.

Air Cathodes

In embodiments of the invention, an air cathode adapted from those usedin Zn/Air batteries or low temperature fuel cells (e.g., PEM), and whichare well known to those of skill in that art, may be used as the aircathode in the inventive Li/air battery cells described herein.

In various embodiments, the instant Li/air cell comprises an air cathodecomprising, at least, a first sectional layer comprising a first gasdiffusion (e.g., Teflon) backing layer (which is positioned adjacent tothe air side in the cell), a wet-proof gas-supply layer, for examplemade of Teflon and acetylene black, a metal screen current collector andan active carbon layer.

The type of metal used for the current collector may be chosen based onits chemical stability in the cell, specifically its stability incontact with the aqueous catholyte. In specific embodiments the metalscreen current collector may be composed of stainless steel, nickelcopper, titanium or alloys thereof.

One or more electrocatalysts may be used. In some embodiments a singleelectrocatalyst is used which is capable of facilitating both the oxygenevolution reaction (OER) on charge and the oxygen reduction reaction(OER) on discharge. In other embodiments two or more catalysts areincorporated in the cathode. A first electrocatalyst material forcatalyzing the OER and stable down to, and preferably beyond, thepotential at which ORR takes place; and a second electrocatalyst forcatalyzing the ORR and stable up to, and preferably beyond, thepotential at which OER takes place.

The active carbon layer may contain the electrocatalyst or may beuncatalyzed. One particularly suitable electrocatalyst that may be usedto catalyze one or both of the OER or ORR is iridium oxide compoundsincluding compositionally pure iridium oxide and solid solutioncompounds thereof.

Air cathodes suitable for use herein are described in detail elsewhere.In particular U.S. Pat. No. 7,645,543; U.S. Pat. No. 7,282,295; and U.SPatent Publication No.: US 2009/0311596 all of which are herebyincorporated by reference in their entirety, and in particular for theirdescription of air cathode structure and composition.

Itemized Specific Embodiments

The following is an itemization of some specific embodiments of theinvention:

1. An alkali metal/oxygen electrochemical energy storage cell, the cellcomprising:an anode comprising an alkali metal electroactive component material;a cathode on or at which molecular oxygen is electro-reduced during celldischarge, the cathode in alkali metal ion communication with the anode;a catholyte comprising water and one or more evaporative-loss resistantand/or polyprotic active compounds dissolved in water that partake in acell discharge reaction and effectuate cathode capacity for discharge inthe acidic region, the catholyte in contact with said cathode; anda protective membrane architecture interposed between the cathode andthe anode, the protective membrane architecture having a first andsecond major surface, the first surface adjacent to the cathode and incontact with the catholyte and the second surface adjacent to the anode;and

wherein the protective membrane architecture solely allows throughtransport of the alkali metal ion and prevents liquids from contactingthe alkali metal anode.

2. The cell of item 1, wherein the catholyte comprises:water; anda carboxylic acid dissolved in water, the acid represented by thefollowing general formula

wherein R¹ represents an organic radical;wherein R² represents H or an organic radical; andwherein R³ represents H or an organic radical.3. The cell of item 2, wherein at least one of the organic radicalsrepresented by R¹, R² or R³ comprises a carboxyl group.4. The cell of item 3, wherein the carboxylic acid is malonic acid, thusR² and R³ represent H and R¹ represents a carboxyl group.5. The cell of item 2, wherein at least one of R¹, R² and R³ representsan organic radical selected from the group consisting of an optionallysubstituted C₁-C₁₀ alkyl group, optionally substituted C₂-C₁₀ alkenylgroup, optionally substituted C₂-C₁₀ alkynyl group.6. The cell of item 2, wherein at least one of R¹, R² and R³ representsan organic radical selected from the group consisting of an optionallysubstituted C₄-C₁₀ cycloalkyl, optionally substituted C₄-C₁₀cycloalkenyl, and optionally substituted 3-10 membered hetercyclyl.7. The cell of item 2, wherein at least one of R¹, R² and R³ representan organic radical selected from the group consisting of an optionallysubstituted carbo- and heterocyclic 5-10 membered aryl.8. The cell of item 2, wherein the carboxylic acid is selected from thegroup consisting of malonic acid, glutaric acid, and methylsuccinicacid.9. The cell of item 2, wherein the equivalent weight of the acid thatpartakes in the cell discharge reaction, is selected from the range ofvalues consisting of 50-70 g/equivalent of H+; 71-90 g/equivalent of H+;91-110 g/equivalent of H⁺.10. The cell of item 2, wherein the concentration of the carboxylic acidin the catholyte is greater than 1 molar.11. The cell of item 2, wherein the concentration of the carboxylic acidin the catholyte is 0.5 molar or greater.12. The cell of item 2, wherein the concentration of the carboxylic acidin the catholyte is 0.25 molar or greater.13. The cell of item 2, wherein the concentration of the carboxylic acidin the catholyte is between 0.05 molar and 1 molar.14. The cell of item 2, wherein the catholyte further comprises solidphase carboxylic acid in contact with its solution.15. The cell of item 2, wherein the catholyte is saturated with thecarboxylic acid.16. The cell of item 2, wherein the carboxylic acid is malonic acid.17. The cell of item 16, wherein the concentration of malonic acid inthe catholyte is selected from the molar range consisting of 0.5 molarto 2 molar, 2 molar to 4 molar, and greater than 4 molar.18. The cell of item 2, further comprising a lithium salt dissolved inwater.19. The cell of items 18, wherein the lithium salt is selected from thegroup consisting of lithium nitrate, lithium sulfate, and lithiumperchlorate.20. The cell of item 18, wherein the lithium salt is lithium nitrate.21. The cell of item 18, wherein the concentration of the lithium saltin the catholyte is selected from the molar range consisting of 0.5molar to 1 molar, 1 molar to 2 molar, and greater than 2 molar.22. The cell of item 20, wherein the carboxylic acid is malonic acid andthe concentration of malonic acid in the catholyte is about 2 molar orabout 4 molar or therebetween, and further wherein the concentration ofthe lithium nitrate salt is about 2 molar.23. The cell of item 20, wherein the carboxylic acid is malonic acid andthe concentration of malonic acid in the catholyte is about 0.5 molar,and further wherein the concentration of the lithium nitrate salt isabout 1 molar.24. The cell of any of items 1-23, wherein the alkali metal/oxygenelectrochemical energy storage cell is a lithium oxygen battery cell.25. The cell of item 24, wherein the lithium oxygen battery cell is alithium air battery cell open to ambient air for accessing active oxygenthat is reduced at the cathode of the cell during discharge.26. The cell any of items 1-25 wherein the pH of the catholyte prior toinitial discharge is less than 7, less than 6, less than 5, less than 4,or less than 3.27. The cell any of items 1-25 wherein the pH of the catholyte prior toinitial discharge is in the range of 7 to 3, in the range of 6 to 3, inthe range of 5 to 3, or in the range of 4 to 3.28. The cell of item 1, wherein the catholyte comprises:water; andan amino acid dissolved in water, the amino acid represented by thefollowing general formula

wherein R represents an aliphatic or aromatic optionally substitutedorganic divalent radical.29. The cell of item of 28, wherein the nitrogen atom of the amino groupis protonated with a proton of a strong acid yielding amino acid aminiumsalt.30. The cell of item 29, wherein the amino acid aminium salt is selectedfrom the group consisting of an amino acid nitrate, an amino acidhydrosulfate, an amino acid sulfate, and an amino acid perchlorate.31. The cell of item 28, wherein the amino acid is selected from thegroup glycine, alanine, proline, and aminomalonic acid.32. The cell of item 1, wherein the catholyte comprises:

water; and

a hydroxy acid dissolved in water, the hydroxy acid represented by thefollowing general formula

wherein R represents an aliphatic or aromatic optionally substitutedorganic divalent radical.33. The cell of item 32, wherein the acid is selected from the groupconsisting of citric acid, glycolic acid, lactic acid,2-hydroxypropionic acid, 3-hydroxypropionic acid, 2-hydroxybutyric acid,3-hydroxybutyric acid.34. The cell of item 32, wherein the carboxylic acid is citric acid.35. The cell of item 34, wherein the concentration of citric acid isbetween 0.5 molar to 2 molar.36. The cell of item 1, wherein the catholyte comprises:

a metal acid salt of a polycarboxylic acid comprising a carboxylateanion, one or more acidic protons, and one or more metal cations or aneutral or acid onium salt of polycarboxylic acid comprising acarboxylate anion, one or more onium cations, and one or more acidicprotons if the onium salt is an acid onium salt;

wherein the metal acid salt or the onium neutral or acid salt is presentin the catholyte prior to actively operating the battery cell.37. The cell of item 36, wherein the cation of the metal acid salt isthe alkali metal cation.38. The cell of item 36, wherein the cation of the metalacid salt islithium.39. The cell of item 36, wherein the polycarboxylic acid from which theacid salt is derived has a first acidic proton that is neutralized inthe partial neutralization process and a second acidic proton that isnot neutralized said process, and further wherein the second acidicproton actively partakes in the cell discharge reaction.40. The cell of item 36, wherein the metal acid salt is an alkali metalhydrogen carboxylate.41. The cell of item 36, wherein the metal acid salt is a lithiumhydrogen carboxylate.42. The cell of item 36, wherein the metal acid salt is selected fromthe group consisting of lithium hydrogen malonate, lithium dihydrogencitrate, and dilithium hydrogen citrate.43. The cell of item 36, wherein the acid onium salt is an acid aminiumsalt where an aminium cation contains nitrogen atom protonated by apolycarboxylic acid.44. The cell of item 43, wherein the acid aminium salt has two types ofacidic protons: a first type on a carboxylic group, and a second type ona primary, secondary, or tertiary ammonium cation, both of which areavailable to actively partake in a discharge reaction of the cell.45. The cell of item 43, wherein the aminium cation is imidazolium.46. The cell of item 43, wherein the acid aminium salt is an imidazoliumhydrogen carboxylate.47. The cell of item 43, wherein the aminium acid salt is selected fromthe group consisting of imidazolium hydrogen malonate, imidazoliumhydrogen citrate, and imidazolium dihydrogen citrate.48. The cell of item 1, further comprising a non-aqueous protic solvent.49. The cell of item 48, wherein the non-aqueous protic solvent is amono- or polyatomic alcohol.50. The cell of item 1, further comprising a non-aqueous aproticsolvent.51. The cell of item 50, wherein the non-aqueous aprotic solvent isselected from the group consisting of DMF and DMSO.52. The cell of item 1, wherein the catholyte comprises:

water; and

an inorganic acid salt selected from the group consisting of lithiumdihydrogen phosphate and lithium hydrogen selenite, and combinationsthereof.

53. The cell of item 1, wherein the catholyte comprises:

water;

an aprotic solvent; and

a carboxylic acid derivative, wherein the hydroxyl moiety of thecarboxyl group is replaced by an atom or a group of atoms comprising anelectronegative atom, and the chemical group is not a hydroxyl group.

54. The cell of item 53, wherein said electronegative atom is selectedfrom the group consisting of nitrogen, oxygen or a halogen.55. The cell of item 53, wherein the carboxylic acid derivative isrepresented by the following general formula:

wherein R represents an aliphatic or aromatic optionally substitutedorganic radical and X represents atom or a group of atoms comprising anelectronegative atom, and further wherein the group X is not representedby OH

-   -   or nitrile represented by the general formula

R—CN,

-   -   where R is an organic aliphatic or aromatic radical.        56. The cell of item 55, wherein said electronegative atom is        selected from the group consisting of nitrogen, oxygen and        halogen.        57. The cell of item 55, wherein carboxylic acid derivative is        selected from the group consisting of an acyl halide, an        anhydride, an ester, an amide, and a nitrile.        58. The cell of item 53, wherein the carboxylic acid derivative        is an organic ester represented by the general formula:

wherein R¹ represents an aliphatic or aromatic optionally substitutedorganic radical; andwherein R² represents an aliphatic or aromatic optionally substitutedorganic radical.59. The cell of item 58:wherein R¹ represents the organic radical selected from the groupconsisting an optionally substituted C₁-C₁₀ alkyl group, optionallysubstituted C₂-C₁₀ alkenyl group, optionally substituted C₂-C₁₀ alkynylgroup, optionally substituted C₄-C₁₀ cycloalkyl, optionally substitutedC₄-C₁₀ cycloalkenyl, optionally substituted 3-10 membered hetercyclyl,optionally substituted carbo- and heterocyclic 5-10 membered aryl,optionally substituted carbonyl.wherein R² an optionally substituted C₁-C₁₀ alkyl group, optionallysubstituted C₂-C₁₀ alkenyl group, optionally substituted C₂-C₁₀ alkynylgroup, optionally substituted C₄-C₁₀ cycloalkyl, optionally substitutedC₄-C₁₀ cycloalkenyl, optionally substituted 3-10 membered heterocyclyl,optionally substituted carbo- and heterocyclic 5-10 membered aryl,optionally substituted carbonyl.60. The cell of item 58:wherein R¹ represents the organic radical selected from the groupconsisting of benzyl, phenyl, —COOR, —CH₂COOR, —CH₂CH₂COOR,CH₂CH₂CH₂COOR, —CH₂CN, —CH₂CF₃, CCl₂, C₅H₁₁, and C₅H₁₃;wherein R² represents the organic radical selected from the groupconsisting of —CH₂—CH₂OH, —CH₂—CH₂OR, —CH₂—CH(OH)—CH₂OH,—CH₂—CH(OR)—CH₂OH, —CH₂—CH(OH)—CH₂OR, —CH₂—CH(OR)—CH₂OR,—(CH₂)₂—O—(CH₂)₂OR; andwherein R is an aliphatic or aromatic optionally substituted organicradical.61. The cell of item 58, wherein the carboxylic acid derivative is anorganic ester selected from the group consisting of diethylene glycoldibenzoate, 2-methoxyethyl cyanoacetate, ethylene glycol monosalicylate,and ethylene brassylate.62. The cell of item 53, wherein the carboxylic acid derivative is alactone.63. The cell of item 62, wherein the lactone is represented by thegeneral formula

wherein n is from 2 to 4.wherein R¹ represents an aliphatic or aromatic optionally substitutedorganic radical; andwherein R² represents an aliphatic or aromatic optionally substitutedorganic radical.64. The cell of item 62, wherein the lactone is selected from the groupconsisting of y-butyrolactone, δ-gluconolactone, and glutaric anhydride.65. The cell of item 1, wherein the catholyte comprises:

water;

an aprotic solvent; and

an ester of an inorganic acid represented by the general formulaX(OR)_(n)wherein R is an aliphatic or aromatic optionally substituted organicradical;X=N(═O)₂, S(═O)₂, or P═O; andn is basicity of an acid from which the ester was derived.66. The cell of item 65, wherein the ester is ester of sulfuric acidthat is represented by the general formula:

wherein R¹ is an aliphatic or aromatic optionally substituted organicradical; andwherein R² is an aliphatic or aromatic optionally substituted organicradical.67. The cell of item 65, wherein the ester is ester of nitric acid thatis represented by the general formula:

wherein R is an aliphatic or aromatic optionally substituted organicradical.68. The cell of item 65, wherein the ester is phosphate ester that isrepresented by the following general formula

wherein R¹ is an aliphatic or aromatic optionally substituted organicradical;wherein R² is selected from the group consisting of an aliphatic oraromatic optionally substituted organic radical, and hydrogen atom; andwherein R³ is selected from the group consisting of an aliphatic oraromatic optionally substituted organic radical, and hydrogen atom.69. The cell of item 68, wherein the phosphate ester is a phosphatetriester; andwherein R² is an aliphatic or aromatic optionally substituted organicradical; andwherein R³ is an aliphatic or aromatic optionally substituted organicradical.70. The cell of item 69 wherein the phosphate triester is selected fromthe group consisting of trimethyl phosphate, triethyl phosphate,tripropyl phosphate, tributyl phosphate, and tris(2-butoxyethyl)phosphate.71. The cell of item 68, wherein the phosphate ester is a phosphatediester; andwherein R² is an hydrogen atom and R³ is an aliphatic or aromaticoptionally substituted organic radical.72. The cell of item 1, wherein the catholyte comprises:

water; and

an organic acid or an amide comprising an element selected from thegroup consisting of sulfur, nitrogen and phosphorus.73. The cell of item 70, wherein the organic acid or amide is sulfonicacid.74. The cell of item 71, wherein the sulfonic acid is represented by thefollowing general formula

andR is selected from the group consisting of an aliphatic and an aromaticoptionally substituted organic radical.75. The cell of item 73, wherein the sulfonic acid is selected from thegroup consisting of:MES (2-(N-Morpholino)ethanesulfonic acid), MOPS(3-(N-Morpholino)propanesulfonic acid), BES(N,N-Bis(2-hydroxyethyl)-2-aminoethanesulfonic acid), TES(2-[(2-Hydroxy-1,1-bis(hydroxymethyl)ethyl)amino]ethanesulfonic acid),TAPSO (2-Hydroxy-3-[tris(hydroxymethyl)methylamino]-1-propanesulfonicacid), N-[Tris(hydroxymethyl)methyl]-3-amino-2-hydroxypropanesulfonicacid), HEPPS (4-(2-Hydroxyethyl)-1-piperazinepropanesulfonic acid), CHES(2-(Cyclohexylamino)ethanesulfonic acid), and 3-Aminobenzenesulfonicacid.76. The cell of item 75, wherein the sulfonic acid is selected from thegroup consisting of MES, MOPS, and HEPPS.77. The cell of item 72 wherein the organic acid or amide is amide ofsulfonic acid (sulfonamide).78. The cell of item 77, wherein the sulfonamide is represented by thegeneral formula

wherein R¹ is an aliphatic or aromatic optionally substituted organicradical; andwherein R² is an aliphatic or aromatic optionally substituted organicradical.79. The cell of item 78, wherein the sulfonamide is selected from thegroup consisting of o-, m-, or p-aminobenzenesulfonamide; o-, m-, orp-methylbenzenesulfonamide, o-, m-, or p-cyanobenzenesulfonamide, and4,4′-diaminobenzenesulfanilide.80. The cell of item 1, wherein the catholyte comprises:water; anda phenol represented by the general formula

wherein R¹-R⁵ are an aliphatic or aromatic optionally substitutedorganic radical.81. The cell of item 80, wherein the substituents R¹, R², R³, R⁴, R⁵ areselected from the group consisting of H, OH, CH₃, C₂H₅, C₃H₇, NH₂, NO₂,CN, COOH, SO₃H, C(R)═O, F, Cl, Br, I, CF₃, N(R)₃ ⁺, COOR, CONH₂, CCl₃,OR, N(R)₂; andwherein R is an aliphatic or aromatic optionally substituted organicradical.82. The cell of item 80, wherein the phenol is selected from the groupconsisting of resorcinol, 2-methylresorcinol, gallic acid,4-nitrocathecol, 4-hydroxybenzoic acid, 2-nitroresorcinol.83. The cell of item 80, wherein the phenol is a-resorcylic acid orα-resorcylonitrile.84. The cell of item 1, wherein the catholyte comprises:

water; and

an aminium salt dissolved in water.85. The cell of item 84, wherein the aminium salt is represented by thegeneral formula (HNR¹R²R³)⁺X⁻, and X⁻ represents acid residue (anion),R¹, R² and R³ may be hydrogen atom, and at least one of R¹, R² and R³ isan aliphatic or aromatic optionally substituent organic radical.86. The cell of item 85, wherein X⁻ is an inorganic anion selected fromthe group of nitrate, perchlorate, and sulfate anions87. The cell of item 85, wherein X⁻ is a nitrate anion.88. The cell of item 84, wherein the salt is selected from anilinenitrate, diethylenetriamine nitrate, ethanolamine nitrate,2-methyl-1-pyrroline nitrate, methoxyamine nitrate, N-methoxymethylaminenitrate, 1-benzoylpiperazine nitrate, N-methylhydroxylamine nitrate,2-aminocyanopropane nitrate, N,N-diethylcyanoacetamide nitrate,2,2-diethylaminopropionitrile nitrate, 2-amino-2-cyanopropane,dimethylaminocetonitrile nitrate, piperazine dinitrate,N,N-dimethylethylenediamine dinitrate, N-ethylmorpholine nitrate, andtriethanolamine nitrate89. The cell of item 84, wherein the salt is selected from the groupconsisting of salts of N-heterocyclic aliphatic or aromatic compounds.90. The cell of item 84, wherein salt is nitrate.91. The cell of item 90, wherein the salt is selected from the groupconsisting of imidazolium nitrate, 2-methylimidazolium nitrate,4-hydroxymethyl imidazolium nitrate, 4-hydroxybenzimidazolium nitrate,4-methoxybenzimidazolium nitrate, 4-(N-methylacetamido)pyridiniumnitrate, o-, m-, p-methylpyridinium nitrate, o-, m-, p-ethylpyridiniumnitrate, 2-methoxypyridinium nitrate, 3-methoxypyridinium nitrate,3-hydroxypyridinium nitrate, 4-hydroxypyridinium nitrate,3-fluoropyridinium nitrate, 3-bromopyridinium nitrate,3-sulfoxypyridinium nitrate, 3-aminopyridazinium nitrate,3-carboxypyridinium nitrate, 4-methoxypyridazinium nitrate, and2-amino-4,6-dimethyl pyrazinium nitrate.92. The cell of item 91, wherein the salt is imidazolium nitrate.93. The cell of item 1, wherein the catholyte comprises:

water; and

an ammonium salt.

94. The cell of item 93, wherein the ammonium salt is represented by thegeneral formula (NH₄ ⁺)X⁻, wherein X⁻ is the acid residue anion.95. The cell of item 1, wherein the catholyte comprises:

water; and

a first salt dissolved in water, the salt derived from strong acid andweak base.

96. The cell of item 95, wherein the first salt is a nitrate.97. The cell of item 96 wherein the first salt is selected from thegroup consisting of zinc nitrate and magnesium nitrate.98. The cell of item 95, further comprising a second salt dissolved inwater, the second salt derived from strong acid and weak base, andfurther wherein the second salt composition is different than that ofthe first salt.99. The cell of item 98, wherein the second is salt selected from thegroup consisting of zinc nitrate and magnesium nitrate.100. The cell of item 99, wherein prior to initial cell discharge themolar concentration of dissolved magnesium nitrate is at least fivetimes larger than the molar concentration of dissolved zinc nitrate.101. The cell of item 100, wherein the concentration of magnesiumnitrate is in the range of 2-3 molar and the concentration of zincnitrate is in the range of 0.1 to 1 molar.102. The cell of item 99, further comprising a lithium salt.103. The cell of item 102, wherein the lithium salt is lithium nitrate.104. The cell of item 103, wherein the catholyte formulation is selectedfrom the group consisting of: i) the first salt about 2.5 molar, thesecond salt about 0.5 molar and the lithium nitrate about 1 molar; ii)the first salt about 2.8 molar, the second salt about 0.2 molar and thelithium nitrate about 1 molar; iii) the first salt about 2.95 molar, thesecond salt about 0.05 molar and the lithium nitrate about 1 molar.105. The cell of item 104, wherein the combined molarity of the firstand second salt is about 3 molar and the lithium nitrate about 1 molar.106. The cell of item 1, wherein the catholyte comprises:

water; and

an amphoteric hydroxide dissolved in water.

107. The cell of item 102 wherein the amphoteric hydroxide is selectedfrom the group consisting of zinc hydroxide and aluminum hydroxide.108. The cell of item 1, wherein the catholyte comprises:

water; and

a polyprotic organic acid dissolved in water.

109. The cell of item 108, wherein prior to initial discharge the acidis partially neutralized.110. The cell of item 1, wherein the catholyte comprises:

water; and

a chemical species dissolved in water, wherein said chemical speciesundergoes an alkaline hydrolysis via reaction with a cell dischargeproduct over the course of cell discharge.

111. The cell of item 1, wherein the catholyte comprises:

water; and

an organic acid having a vapor pressure less than that of acetic acid.

112. The cell of item 111, wherein the vapor pressure of the acid isless than 1 mmHg.113. The cell of item 111, wherein the vapor pressure of the acid isless than 10³ mmHg.114. The cell of item 1, wherein the cathode further comprises a singlecatalyst composition, not platinum, that catalyzes both the oxygenevolution reaction and the oxygen reduction reaction.115. The cell of item 1, wherein the cathode comprises a first catalystcomposition and a second catalyst composition, the first catalystcomposition catalyzing the oxygen evolution reaction during cell chargeand the second catalyst composition catalyzing the oxygen reductionreaction during cell discharge.116. A method of making or using an alkali metal/oxygen electrochemicalenergy storage cell, the method comprising the steps of:providing,an anode comprising an alkali metal electroactive component material,a cathode on or at which molecular oxygen is electro-reduced during celldischarge, the cathode in alkali metal ion communication with the anode,a protective membrane architecture interposed between the cathode andthe anode, the protective membrane architecture having a first andsecond major surface, the first surface adjacent to the cathode and thesecond surface adjacent to the anode, and

wherein the protective membrane architecture solely allows throughtransport of the alkali metal ion and prevents liquids from contactingthe alkali metal anode; and

dispensing or flowing a catholyte into contact with the cathode, thecatholyte comprising water and one or more evaporative-loss resistantand/or polyprotic active compounds dissolved in water that partake in acell discharge reaction and effectuate cathode capacity for discharge inthe acidic region.117. The method of item 116, further comprising

discharging the cell to a capacity sufficient to cause the catholyte tobecome basic;

charging said battery cell to a capacity sufficient to cause thecatholyte to become acidic; and

discharging the battery cell.

118. The method of item 117, wherein the initial composition of thecatholyte is sufficiently acidic to cause decomposition of solidcarbonate discharge products, and further wherein said charging stepinvolves charging the cell to a sufficient capacity to cause thecatholyte pH to reach a level of acidity sufficient to dissolve anddecompose carbonate.119. The method of item 118, wherein the charging proceeds according toa protocol that includes holding the voltage constant or maintaining aconstant current whence the pH of the catholyte is sufficiently acidicto decompose enough carbonate to bring the cell capacity for thesubsequent discharge to more than 90% of the cell's initial ratedcapacity.120. A method of making an initial catholyte for use in an alkali metaloxygen electrochemical energy storage cell, the method comprising thesteps of:

-   -   providing water;    -   dissolving a polycarboxylic acid in water; and

dissolving a chemical species in water that undergoes an electrondonor-acceptor reaction with the polycarboxylic acid.

Alternative Embodiments

While the invention is described primarily in terms of Li and Li alloysanodes, other alkali metal anodes, in particular sodium (Na) may also beused in alternative embodiments. In such an alternative embodiment, theprotective membrane architecture on the anode is configured for highionic conductivity of the alkali metal ions of the anode material. Forexample, a protective membrane architecture for a Na metal anode mayinclude a solid electrolyte layer composed of Nasicon.

CONCLUSION

Although the foregoing invention has been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications may be practiced within the scope of theinvention, in particular the appended claims. It should be noted thatthere are many alternative ways of implementing both the devices andmethods of the present invention. Accordingly, the present embodimentsare to be considered as illustrative and not restrictive, and theinvention is not to be limited to the details given herein.

1. An alkali metal/oxygen electrochemical energy storage cell, the cellcomprising: an anode comprising an alkali metal electroactive componentmaterial; an open-to-ambient-air cathode on or at which molecular oxygenobtained from the ambient air is electro-reduced during cell discharge,the cathode in alkali metal ion communication with the anode; an aqueouscatholyte comprising water and one or more organic polyprotic activecompounds dissolved in water that partake in a cell discharge reactionand effectuate cathode capacity for discharge below pH 7, the catholytein contact with said cathode, wherein the one or more organic polyproticactive compounds comprises an organic polyprotic acid that dissociatesover the course of discharge, thus yielding two or more active protonsper acid molecule in the catholyte that partake in the cell reaction asthe discharge proceeds; and a protective membrane architectureinterposed between the cathode and the anode, the protective membranearchitecture having a first and a second major surface, the firstsurface adjacent to the cathode and in contact with the catholyte andthe second surface adjacent to the anode; and wherein the protectivemembrane architecture solely allows through transport of the alkalimetal ion and prevents liquids from contacting the alkali metal anode;and wherein the organic polyprotic acid comprises a species thatdissociates over the course of discharge yielding two or more activeprotons per acid molecule in the catholyte that partake in the cellreaction as the discharge proceeds.
 2. The cell of claim 1, wherein thecatholyte comprises: water; and the organic polyprotic acid is acarboxylic acid dissolved in water, the acid represented by thefollowing general formula

wherein R¹ represents an organic radical; wherein R² represents H or anorganic radical; and wherein R³ represents H or an organic radical. 3.(canceled)
 4. The cell of claim 2, wherein the carboxylic acid ismalonic acid, thus R² and R³ represent H and R¹ represents a carboxylgroup.
 5. The cell of claim 2, wherein at least one of R¹, R² and R³represents an organic radical selected from the group consisting of anoptionally substituted C₁-C₁₀ alkyl group, optionally substituted C₂-C₁₀alkenyl group, optionally substituted C₂-C₁₀ alkynyl group.
 6. The cellof claim 2, wherein at least one of R¹, R² and R³ represents an organicradical selected from the group consisting of an optionally substitutedC₄-C₁₀ cycloalkyl, optionally substituted C₄-C₁₀ cycloalkenyl, andoptionally substituted 3-10 membered heterocyclyl.
 7. The cell of claim2, wherein at least one of R¹, R² and R³ represent an organic radicalselected from the group consisting of an optionally substituted carbo-and heterocyclic 5-10 membered aryl.
 8. The cell of claim 2, wherein thecarboxylic acid is selected from the group consisting of malonic acid,glutaric acid, and methylsuccinic acid.
 9. The cell of claim 1, whereinthe equivalent weight of the acid that partakes in the cell dischargereaction, is selected from the range of values consisting of 50-70g/equivalent of H⁺; 71-90 g/equivalent of H⁺; 91-110 g/equivalent of H⁺.10-12. (canceled)
 13. The cell of claim 1, wherein the concentration ofthe carboxylic acid in the catholyte is between 0.05 molar and 1 molar.14. The cell of claim 1, wherein the catholyte further comprises solidphase carboxylic acid in contact with its solution.
 15. The cell ofclaim 1, wherein the catholyte is saturated with the carboxylic acid.16. The cell of claim 1, wherein the alkali metal electroactivecomponent material comprises lithium.
 17. The cell of claim 1, whereinthe anode is selected from the group consisting of lithium metal,lithium metal alloy, and lithium intercalation material.
 18. The cell ofclaim 1, wherein the anode is a lithium metal sheet. 19-120. (canceled)